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Brian Space - One of the best experts on this subject based on the ideXlab platform.
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Time Correlation Function modeling of third order sum frequency vibrational spectroscopy of a charged surface water interface
Journal of Physical Chemistry B, 2015Co-Authors: Anthony J. Green, Brian SpaceAbstract:Sum frequency vibrational spectroscopy (SFVS), a second-order optical process, is interface-specific in the dipole approximation [Perry, A.; Neipert, C.; Moore, P.; Space, B. Chem. Rev. 2006, 106, 1234−1258; Richmond, G. L. Chem. Rev. 2002, 102, 2693–2724; Byrnes, S. J.; Geissler, P. L.; Shen, Y. R. Chem. Phys. Lett. 2011, 516, 115–124]. At charged interfaces, the experimentally detected signal is a combination of enhanced second-order and static-field-induced third-order contributions due to the existence of a static field. Evidence of the importance/relative magnitude of this third-order contribution is seen in the literature [Ong, S.; Zhao, X.; Eisenthal, K. B. Chem. Phys. Lett. 1992, 191, 327−335; Zhao, X.; Ong, S.; Eisenthal, K. B. Chem. Phys. Lett. 1993, 202, 513–520; Shen, Y. R. Appl. Phys. B: Laser Opt. 1999, 68, 295–300], but a molecularly detailed approach to separately calculating the second- and third-order contributions is difficult to construct. Recent work presented a novel molecular dynami...
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Time Correlation Function Modeling of Third-Order Sum Frequency Vibrational Spectroscopy of a Charged Surface/Water Interface
Journal of Physical Chemistry B, 2015Co-Authors: Anthony J. Green, Brian SpaceAbstract:Sum frequency vibrational spectroscopy (SFVS), a second-order optical process, is interface-specific in the dipole approximation [ Perry , A. ; Neipert , C. ; Moore , P. ; Space , B. Chem. Rev. 2006 , 106 , 1234 - 1258 ; Richmond , G. L. Chem. Rev. 2002 , 102 , 2693 - 2724 ; Byrnes , S. J. ; Geissler , P. L. ; Shen , Y. R. Chem. Phys. Lett. 2011 , 516 , 115 - 124 ]. At charged interfaces, the experimentally detected signal is a combination of enhanced second-order and static-field-induced third-order contributions due to the existence of a static field. Evidence of the importance/relative magnitude of this third-order contribution is seen in the literature [ Ong , S. ; Zhao , X. ; Eisenthal , K. B. Chem. Phys. Lett. 1992 , 191 , 327 - 335 ; Zhao , X. ; Ong , S. ; Eisenthal , K. B. Chem. Phys. Lett. 1993 , 202 , 513 - 520 ; Shen , Y. R. Appl. Phys. B: Laser Opt. 1999 , 68 , 295 - 300 ], but a molecularly detailed approach to separately calculating the second- and third-order contributions is difficult to construct. Recent work presented a novel molecular dynamics (MD)-based theory that provides a direct means to calculate the third-order contributions to SFVS spectra at charged interfaces [ Neipert , C. ; Space , B. J. Chem. Phys. 2006 , 125 , 224706 ], and a hyperpolarizability model for water was developed as a prerequisite to practical implementation [ Neipert , C. ; Space , B. Comput. Lett. 2007 , 3 , 431 - 440 ]. Here, these methods are applied to a highly abstracted/idealized silica/water interface, and the results are compared to experimental data for water at a fused quartz surface. The results suggest that such spectra have some quite general spectral features.
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generalized computational Time Correlation Function approach quantifying quadrupole contributions to vibrationally resonant second order interface specific optical spectroscopies
Journal of Physical Chemistry C, 2007Co-Authors: Brian Space, Alfred B. RoneyAbstract:Second-order optical measurements are interface specific (vanishing in isotropic media) in the dipole approximation. Given this approximation, there has been debate, and it is of much interest, to determine the quantitative contribution of bulk media to the second-order optical spectra. Simple estimates and extant experiments have clearly demonstrated that quadrupole contributions can be on the order of dipole contributions for some liquids. However, no definitive set of criteria exists to determine when this will be the case. To this end, a computationally tractable Time Correlation Function formalism is developed that goes beyond the dipole approximation, accounting for dipole, dipole−quadrupole, and pure quadrupole contributions. This theory generalizes an earlier description by both avoiding the rotating wave approximation and including higher order quadrupole contributions. It is, therefore, capable of also describing sum frequency vibrational spectroscopy (SFVS) spectra at low and intermediate frequ...
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Generalized computational Time Correlation Function approach: Quantifying quadrupole contributions to vibrationally resonant second-order interface-specific optical spectroscopies
Journal of Physical Chemistry C, 2007Co-Authors: Christine Neipert, Brian Space, Alfred B. RoneyAbstract:Second-order optical measurements are interface specific (vanishing in\nisotropic media) in the dipole approximation. Given this approximation,\nthere has been debate, and it is of much interest, to determine the\nquantitative contribution of bulk media to the second-order optical\nspectra. Simple estimates and extant experiments have clearly\ndemonstrated that quadrupole contributions can be on the order of dipole\ncontributions for some liquids. However, no definitive set of criteria\nexists to determine when this will be the case. To this end, a\ncomputationally tractable Time Correlation Function formalism is\ndeveloped that goes beyond the dipole approximation, accounting for\ndipole, dipole-quadrupole, and pure quadrupole contributions. This\ntheory generalizes an earlier description by both avoiding the rotating\nwave approximation and including higher order quadrupole contributions.\nIt is, therefore, capable of also describing sum frequency vibrational\nspectroscopy (SFVS) spectra at low and intermediate frequencies where\nequally interesting phenomena occur. Further, to date, no implementation\nmodels have been proposed to calculate quadrupolar contributions to SFVS\nsignals. Thus, such an approach is presented that is appropriate for use\nin conjunction with molecular dynamics methods and makes calculating\nquadrupolar contributions for realistic interfaces possible.
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a Time Correlation Function theory describing static field enhanced third order optical effects at interfaces
Journal of Chemical Physics, 2006Co-Authors: Christine Neipert, Brian SpaceAbstract:Sum vibrational frequency spectroscopy, a second order optical process, is interface specific in the dipole approximation. At charged interfaces, there exists a static field, and as a direct consequence, the experimentally detected signal is a combination of enhanced second and static field induced third order contributions. There is significant evidence in the literature of the importance/relative magnitude of this third order contribution, but no previous molecularly detailed approach existed to separately calculate the second and third order contributions. Thus, for the first Time, a molecularly detailed Time Correlation Function theory is derived here that allows for the second and third order contributions to sum frequency vibrational spectra to be individually determined. Further, a practical, molecular dynamics based, implementation procedure for the derived Correlation Functions that describe the third order phenomenon is also presented. This approach includes a novel generalization of point atomi...
Christine Neipert - One of the best experts on this subject based on the ideXlab platform.
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Generalized computational Time Correlation Function approach: Quantifying quadrupole contributions to vibrationally resonant second-order interface-specific optical spectroscopies
Journal of Physical Chemistry C, 2007Co-Authors: Christine Neipert, Brian Space, Alfred B. RoneyAbstract:Second-order optical measurements are interface specific (vanishing in\nisotropic media) in the dipole approximation. Given this approximation,\nthere has been debate, and it is of much interest, to determine the\nquantitative contribution of bulk media to the second-order optical\nspectra. Simple estimates and extant experiments have clearly\ndemonstrated that quadrupole contributions can be on the order of dipole\ncontributions for some liquids. However, no definitive set of criteria\nexists to determine when this will be the case. To this end, a\ncomputationally tractable Time Correlation Function formalism is\ndeveloped that goes beyond the dipole approximation, accounting for\ndipole, dipole-quadrupole, and pure quadrupole contributions. This\ntheory generalizes an earlier description by both avoiding the rotating\nwave approximation and including higher order quadrupole contributions.\nIt is, therefore, capable of also describing sum frequency vibrational\nspectroscopy (SFVS) spectra at low and intermediate frequencies where\nequally interesting phenomena occur. Further, to date, no implementation\nmodels have been proposed to calculate quadrupolar contributions to SFVS\nsignals. Thus, such an approach is presented that is appropriate for use\nin conjunction with molecular dynamics methods and makes calculating\nquadrupolar contributions for realistic interfaces possible.
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a Time Correlation Function theory describing static field enhanced third order optical effects at interfaces
Journal of Chemical Physics, 2006Co-Authors: Christine Neipert, Brian SpaceAbstract:Sum vibrational frequency spectroscopy, a second order optical process, is interface specific in the dipole approximation. At charged interfaces, there exists a static field, and as a direct consequence, the experimentally detected signal is a combination of enhanced second and static field induced third order contributions. There is significant evidence in the literature of the importance/relative magnitude of this third order contribution, but no previous molecularly detailed approach existed to separately calculate the second and third order contributions. Thus, for the first Time, a molecularly detailed Time Correlation Function theory is derived here that allows for the second and third order contributions to sum frequency vibrational spectra to be individually determined. Further, a practical, molecular dynamics based, implementation procedure for the derived Correlation Functions that describe the third order phenomenon is also presented. This approach includes a novel generalization of point atomi...
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A Time Correlation Function theory describing static field enhanced third order optical effects at interfaces
Journal of Chemical Physics, 2006Co-Authors: Christine Neipert, Brian SpaceAbstract:Sum vibrational frequency spectroscopy, a second order optical process, is interface specific in the dipole approximation. At charged interfaces, there exists a static field, and as a direct consequence, the experimentally detected signal is a combination of enhanced second and static field induced third order contributions. There is significant evidence in the literature of the importance/relative magnitude of this third order contribution, but no previous molecularly detailed approach existed to separately calculate the second and third order contributions. Thus, for the first Time, a molecularly detailed Time Correlation Function theory is derived here that allows for the second and third order contributions to sum frequency vibrational spectra to be individually determined. Further, a practical, molecular dynamics based, implementation procedure for the derived Correlation Functions that describe the third order phenomenon is also presented. This approach includes a novel generalization of point atomic polarizability models to calculate the hyperpolarizability of a molecular system. The full system hyperpolarizability appears in the Time Correlation Functions responsible for third order contributions in the presence of a static field.
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a Time Correlation Function theory of two dimensional infrared spectroscopy with applications to liquid water
Journal of Chemical Physics, 2004Co-Authors: Russell Devane, Christine Neipert, Angela Perry, Christina Ridley, Brian Space, Thomas KeyesAbstract:A theory describing the third-order response Function R(3)(t1,t2,t3), which is associated with two-dimensional infrared (2DIR) spectroscopy, has been developed. R(3) can be written as sums and differences of four distinct quantum mechanical dipole (multi)Time Correlation Functions (TCF’s), each with the same classical limit; the combination of TCF’s has a leading contribution of order ℏ3 and thus there is no obvious classical limit that can be written in terms of a TCF. In order to calculate the response Function in a form amenable to classical mechanical simulation techniques, it is rewritten approximately in terms of a single classical TCF, BR(t1,t2,t3)=〈μj(t2+t1)μi(t3+t2+t1)μk(t1)μl(0)〉, where the subscripts denote the Cartesian dipole directions. The response Function is then given, in the frequency domain, as the Fourier transform of a classical TCF multiplied by frequency factors. This classical expression can then further be quantum corrected to approximate the true response Function, although for ...
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A Time Correlation Function theory of two-dimensional infrared spectroscopy with applications to liquid water
The Journal of Chemical Physics, 2004Co-Authors: Russell Devane, Christine Neipert, Angela Perry, Christina Ridley, Brian Space, Tom KeyesAbstract:A theory describing the third-order response Function R((3))(t(1),t(2),t(3)), which is associated with two-dimensional infrared (2DIR) spectroscopy, has been developed. R((3)) can be written as sums and differences of four distinct quantum mechanical dipole (multi)Time Correlation Functions (TCF's), each with the same classical limit; the combination of TCF's has a leading contribution of order variant Planck's over 2pi (3) and thus there is no obvious classical limit that can be written in terms of a TCF. In order to calculate the response Function in a form amenable to classical mechanical simulation techniques, it is rewritten approximately in terms of a single classical TCF, where the subscripts denote the Cartesian dipole directions. The response Function is then given, in the frequency domain, as the Fourier transform of a classical TCF multiplied by frequency factors. This classical expression can then further be quantum corrected to approximate the true response Function, although for low frequency spectroscopy no correction is needed. In the classical limit, R((3)) becomes the sum of multidimensional Time derivatives of B(R)(t(1),t(2),t(3)). To construct the theory, the response Function's four TCF's are rewritten in terms of a single TCF: first, two TCF's are eliminated from R((3)) using frequency domain detailed balance relationships, and next, two more are removed by relating the remaining TCF's to each other within a harmonic oscillator approximation; the theory invokes a harmonic approximation only in relating the TCF's and applications of theory involve fully anharmonic, atomistically detailed molecular dynamics (MD). Writing the response Function as a single TCF thus yields a form amenable to calculation using classical MD methods along with a suitable spectroscopic model. To demonstrate the theory, the response Function is obtained for liquid water with emphasis on the OH stretching portion of the spectrum. This approach to evaluating R((3)) can easily be applied to chemically interesting systems currently being explored experimentally by 2DIR and to help understand the information content of the emerging multidimensional spectroscopy.
Heather Ahlborn - One of the best experts on this subject based on the ideXlab platform.
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a combined Time Correlation Function and instantaneous normal mode study of the sum frequency generation spectroscopy of the water vapor interface
Journal of Chemical Physics, 2003Co-Authors: Angela Perry, Heather Ahlborn, Brian Space, Preston B MooreAbstract:Theoretical approximations to the interface specific sum frequency generation (SFG) spectrum of O–H stretching at the water/vapor interface are constructed using Time Correlation Function (TCF) and instantaneous normal mode (INM) methods. Both approaches lead to a (SSP polarization geometry) signal in excellent agreement with experimental measurements; the SFG spectrum of the entire water spectrum, both intermolecular and intramolecular, is reported. The observation that the INM spectrum is in agreement with the TCF result implies that motional narrowing effects play no role in the interfacial line shapes, in contrast to the O–H stretching dynamics in the bulk that leads to a narrowed line shape. This implies that (SSP) SFG spectroscopy is a probe of structure with dynamics not represented in the signal. The INM approach permits the elucidation of the molecular basis for the observed signal, and the motions responsible for the SFG line shape are well approximated as local O–H stretching modes. The complexity of the broad structured SFG signal is due to O–H stretching motions facing toward the bulk or vacuum environments that are characteristic of the interface. The success of both approaches suggests that theory can play a crucial role in interpreting SFG spectroscopy at more complex interfaces. It is also found that many-body polarization effects account for most of the observed signal intensity.
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A combined Time Correlation Function and instantaneous normal mode study of the sum frequency generation spectroscopy of the water/vapor interface
Journal of Chemical Physics, 2003Co-Authors: Angela Perry, Heather Ahlborn, Brian Space, Preston MooreAbstract:Theoretical approximations to the interface specific sum frequency\ngeneration (SFG) spectrum of O-H stretching at the water/vapor interface\nare constructed using Time Correlation Function (TCF) and instantaneous\nnormal mode (INM) methods. Both approaches lead to a (SSP polarization\ngeometry) signal in excellent agreement with experimental measurements;\nthe SFG spectrum of the entire water spectrum, both intermolecular and\nintramolecular, is reported. The observation that the INM spectrum is in\nagreement with the TCF result implies that motional narrowing effects\nplay no role in the interfacial line shapes, in contrast to the O-H\nstretching dynamics in the bulk that leads to a narrowed line shape.\nThis implies that (SSP) SFG spectroscopy is a probe of structure with\ndynamics not represented in the signal. The INM approach permits the\nelucidation of the molecular basis for the observed signal, and the\nmotions responsible for the SFG line shape are well approximated as\nlocal O-H stretching modes. The complexity of the broad structured SFG\nsignal is due to O-H stretching motions facing toward the bulk or vacuum\nenvironments that are characteristic of the interface. The success of\nboth approaches suggests that theory can play a crucial role in\ninterpreting SFG spectroscopy at more complex interfaces. It is also\nfound that many-body polarization effects account for most of the\nobserved signal intensity. (C) 2003 American Institute of Physics.
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the effect of isotopic substitution and detailed balance on the infrared spectroscopy of water a combined Time Correlation Function and instantaneous normal mode analysis
Journal of Chemical Physics, 2000Co-Authors: Heather Ahlborn, Brian Space, Preston B MooreAbstract:We have recently demonstrated that simple classical molecular dynamics methods are capable of nearly quantitatively reproducing most of the intermolecular and intramolecular infrared (IR) spectroscopy of water [H. Ahlborn, X. Ji, B. Space, and P. B. Moore, J. Chem. Phys. 111, 10622 (1999)]. Here it is demonstrated that the result is robust by quantitatively reproducing experimentally measured D2O IR spectroscopy utilizing the same models. This suggests that the quantum effects associated with light atom motion are relatively unimportant. Instantaneous normal mode (INM) theory and the Time Correlation Function (TCF) methodology are used in a complimentary fashion to analyze the molecular origin of the IR spectroscopy of deuterated water (D2O). The TCF methods demonstrate that our models of the dynamics and the system dipole are reasonable by successful quantitative comparison of the theoretical spectrum with experimental results. INM methodology is then employed to analyze what condensed phase motions are ...
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a combined instantaneous normal mode and Time Correlation Function description of the optical kerr effect and raman spectroscopy of liquid cs2
Journal of Chemical Physics, 2000Co-Authors: Xing Dong Ji, Stephanidis Constantine, Heather Ahlborn, Brian Space, Yan Zhou, Preston B Moore, L. D. ZieglerAbstract:The depolarized reduced Raman and corresponding optical Kerr effect (OKE) spectral density of ambient CS2 have been calculated by way of Time Correlation Function (TCF) and instantaneous normal mode (INM) methods and compared with experimental OKE data. When compared in the reduced Raman spectrum form, where the INM spectrum is proportional to the squared polarizability derivative weighted density of states (DOS), the INM results agree nearly quantitatively (at all but the lowest frequencies) with the TCF results. Both are in excellent agreement with experimental measurements. The INM signal has a significant contribution from the imaginary INMs. Within our INM theory of spectroscopy the imaginary INMs contribute like the real modes, at the magnitude of their imaginary frequency. When only the real modes are allowed to contribute, and the spectrum is rescaled to account for the missing degrees of freedom, the results are much poorer, as has been observed previously. When the spectra are compared in their ...
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The effect of isotopic substitution and detailed balance on the infrared spectroscopy of water: A combined Time Correlation Function and instantaneous normal mode analysis
The Journal of Chemical Physics, 2000Co-Authors: Heather Ahlborn, Brian Space, Preston MooreAbstract:We have recently demonstrated that simple classical molecular dynamics methods are capable of nearly quantitatively reproducing most of the intermolecular and intramolecular infrared (IR) spectroscopy of water {[}H. Ahlborn, X. Ji, B. Space, and P. B. Moore, J. Chem. Phys. 111, 10622 (1999)]. Here it is demonstrated that the result is robust by quantitatively reproducing experimentally measured D2O IR spectroscopy utilizing the same models. This suggests that the quantum effects associated with light atom motion are relatively unimportant. Instantaneous normal mode (INM) theory and the Time Correlation Function (TCF) methodology are used in a complimentary fashion to analyze the molecular origin of the IR spectroscopy of deuterated water (D2O). The TCF methods demonstrate that our models of the dynamics and the system dipole are reasonable by successful quantitative comparison of the theoretical spectrum with experimental results. INM methodology is then employed to analyze what condensed phase motions are responsible for the observed O-D stretching line shapes. It is surprising that classical models can reproduce the complex spectroscopy of both liquid H2O and D2O, and this result implies that the motions responsible for the signal must be effectively harmonic in nature. This assertion is supported by the drastic impact that is seen on both the intensity and line shape through the choice of detailed balance correction factor that is used to quantum correct the classical vibrational line shape. (C) 2000 American Institute of Physics. {[}S0021-9606(00)50518-2].
Russell Devane - One of the best experts on this subject based on the ideXlab platform.
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Time Correlation Function and finite field approaches to the calculation of the fifth order Raman response in liquid xenon
Journal of Chemical Physics, 2006Co-Authors: Russell Devane, Thomas I.c. Jansen, Brian Space, Tom KeyesAbstract:The fifth order, two-dimensional Raman response in liquid xenon is calculated via a Time Correlation Function (TCF) theory and the numerically exact finite field method. Both employ classical molecular dynamics simulations. The results are shown to be in excellent agreement, suggesting the efficacy of the TCF approach, in which the response Function is written approximately in terms of a single classical multiTime TCF.
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applications of a Time Correlation Function theory for the fifth order raman response Function i atomic liquids
Journal of Chemical Physics, 2005Co-Authors: Russell Devane, Christina Ridley, Brian Space, Thomas KeyesAbstract:Multidimensional spectroscopy has the ability to provide great insight into the complex dynamics and Time-resolved structure of liquids. Theoretically describing these experiments requires calculating the nonlinear-response Function, which is a combination of quantum-mechanical Time Correlation Functions (TCFs), making it extremely difficult to calculate. Recently, a new theory was presented in which the two-dimensional Raman quantum response Function R(5)(t1,t2) was expressed with a two-Time, computationally tractable, classical TCF. Writing the response Function in terms of classical TCFs brings the full power of atomistically detailed molecular dynamics to the problem. In this paper, the new TCF theory is employed to calculate the fifth-order Raman response Function for liquid xenon and investigate several of the polarization conditions for which experiments can be performed on an isotropic system. The theory is shown to reproduce line-shape characteristics predicted by earlier theoretical work.
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Applications of a Time Correlation Function theory for the fifth-order Raman response Function I: Atomic liquids
Journal of Chemical Physics, 2005Co-Authors: Russell Devane, Christina Ridley, Brian Space, Tom KeyesAbstract:Multidimensional spectroscopy has the ability to provide great insight into the complex dynamics and Time-resolved structure of liquids. Theoretically describing these experiments requires calculating the nonlinear-response Function, which is a combination of quantum-mechanical Time Correlation Functions R5(t1,t2) was expressed with a two-Time, computationally tractable, classical TCF. Writing the response Function in terms of classical TCFs brings the full power of atomistically detailed molecular dynamics to the problem. In this paper, the new TCF theory is employed to calculate the fifth-order Raman response Function for liquid xenon and investigate several of the polarization conditions for which experiments can be performed on an isotropic system. The theory is shown to reproduce line-shape characteristics predicted by earlier theoretical work.
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a Time Correlation Function theory of two dimensional infrared spectroscopy with applications to liquid water
Journal of Chemical Physics, 2004Co-Authors: Russell Devane, Christine Neipert, Angela Perry, Christina Ridley, Brian Space, Thomas KeyesAbstract:A theory describing the third-order response Function R(3)(t1,t2,t3), which is associated with two-dimensional infrared (2DIR) spectroscopy, has been developed. R(3) can be written as sums and differences of four distinct quantum mechanical dipole (multi)Time Correlation Functions (TCF’s), each with the same classical limit; the combination of TCF’s has a leading contribution of order ℏ3 and thus there is no obvious classical limit that can be written in terms of a TCF. In order to calculate the response Function in a form amenable to classical mechanical simulation techniques, it is rewritten approximately in terms of a single classical TCF, BR(t1,t2,t3)=〈μj(t2+t1)μi(t3+t2+t1)μk(t1)μl(0)〉, where the subscripts denote the Cartesian dipole directions. The response Function is then given, in the frequency domain, as the Fourier transform of a classical TCF multiplied by frequency factors. This classical expression can then further be quantum corrected to approximate the true response Function, although for ...
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A Time Correlation Function theory of two-dimensional infrared spectroscopy with applications to liquid water
The Journal of Chemical Physics, 2004Co-Authors: Russell Devane, Christine Neipert, Angela Perry, Christina Ridley, Brian Space, Tom KeyesAbstract:A theory describing the third-order response Function R((3))(t(1),t(2),t(3)), which is associated with two-dimensional infrared (2DIR) spectroscopy, has been developed. R((3)) can be written as sums and differences of four distinct quantum mechanical dipole (multi)Time Correlation Functions (TCF's), each with the same classical limit; the combination of TCF's has a leading contribution of order variant Planck's over 2pi (3) and thus there is no obvious classical limit that can be written in terms of a TCF. In order to calculate the response Function in a form amenable to classical mechanical simulation techniques, it is rewritten approximately in terms of a single classical TCF, where the subscripts denote the Cartesian dipole directions. The response Function is then given, in the frequency domain, as the Fourier transform of a classical TCF multiplied by frequency factors. This classical expression can then further be quantum corrected to approximate the true response Function, although for low frequency spectroscopy no correction is needed. In the classical limit, R((3)) becomes the sum of multidimensional Time derivatives of B(R)(t(1),t(2),t(3)). To construct the theory, the response Function's four TCF's are rewritten in terms of a single TCF: first, two TCF's are eliminated from R((3)) using frequency domain detailed balance relationships, and next, two more are removed by relating the remaining TCF's to each other within a harmonic oscillator approximation; the theory invokes a harmonic approximation only in relating the TCF's and applications of theory involve fully anharmonic, atomistically detailed molecular dynamics (MD). Writing the response Function as a single TCF thus yields a form amenable to calculation using classical MD methods along with a suitable spectroscopic model. To demonstrate the theory, the response Function is obtained for liquid water with emphasis on the OH stretching portion of the spectrum. This approach to evaluating R((3)) can easily be applied to chemically interesting systems currently being explored experimentally by 2DIR and to help understand the information content of the emerging multidimensional spectroscopy.
Preston Moore - One of the best experts on this subject based on the ideXlab platform.
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A combined Time Correlation Function and instantaneous normal mode study of the sum frequency generation spectroscopy of the water/vapor interface
Journal of Chemical Physics, 2003Co-Authors: Angela Perry, Heather Ahlborn, Brian Space, Preston MooreAbstract:Theoretical approximations to the interface specific sum frequency\ngeneration (SFG) spectrum of O-H stretching at the water/vapor interface\nare constructed using Time Correlation Function (TCF) and instantaneous\nnormal mode (INM) methods. Both approaches lead to a (SSP polarization\ngeometry) signal in excellent agreement with experimental measurements;\nthe SFG spectrum of the entire water spectrum, both intermolecular and\nintramolecular, is reported. The observation that the INM spectrum is in\nagreement with the TCF result implies that motional narrowing effects\nplay no role in the interfacial line shapes, in contrast to the O-H\nstretching dynamics in the bulk that leads to a narrowed line shape.\nThis implies that (SSP) SFG spectroscopy is a probe of structure with\ndynamics not represented in the signal. The INM approach permits the\nelucidation of the molecular basis for the observed signal, and the\nmotions responsible for the SFG line shape are well approximated as\nlocal O-H stretching modes. The complexity of the broad structured SFG\nsignal is due to O-H stretching motions facing toward the bulk or vacuum\nenvironments that are characteristic of the interface. The success of\nboth approaches suggests that theory can play a crucial role in\ninterpreting SFG spectroscopy at more complex interfaces. It is also\nfound that many-body polarization effects account for most of the\nobserved signal intensity. (C) 2003 American Institute of Physics.
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The effect of isotopic substitution and detailed balance on the infrared spectroscopy of water: A combined Time Correlation Function and instantaneous normal mode analysis
The Journal of Chemical Physics, 2000Co-Authors: Heather Ahlborn, Brian Space, Preston MooreAbstract:We have recently demonstrated that simple classical molecular dynamics methods are capable of nearly quantitatively reproducing most of the intermolecular and intramolecular infrared (IR) spectroscopy of water {[}H. Ahlborn, X. Ji, B. Space, and P. B. Moore, J. Chem. Phys. 111, 10622 (1999)]. Here it is demonstrated that the result is robust by quantitatively reproducing experimentally measured D2O IR spectroscopy utilizing the same models. This suggests that the quantum effects associated with light atom motion are relatively unimportant. Instantaneous normal mode (INM) theory and the Time Correlation Function (TCF) methodology are used in a complimentary fashion to analyze the molecular origin of the IR spectroscopy of deuterated water (D2O). The TCF methods demonstrate that our models of the dynamics and the system dipole are reasonable by successful quantitative comparison of the theoretical spectrum with experimental results. INM methodology is then employed to analyze what condensed phase motions are responsible for the observed O-D stretching line shapes. It is surprising that classical models can reproduce the complex spectroscopy of both liquid H2O and D2O, and this result implies that the motions responsible for the signal must be effectively harmonic in nature. This assertion is supported by the drastic impact that is seen on both the intensity and line shape through the choice of detailed balance correction factor that is used to quantum correct the classical vibrational line shape. (C) 2000 American Institute of Physics. {[}S0021-9606(00)50518-2].
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A combined instantaneous normal mode and Time Correlation Function description of the optical Kerr effect and Raman spectroscopy of liquid CS2
Journal of Chemical Physics, 2000Co-Authors: Xing Dong Ji, Stephanidis Constantine, H Alhborn, Brian Space, Preston Moore, Yan Zhou, L. D. ZieglerAbstract:The depolarized reduced Raman and corresponding optical Kerr effect\n(OKE) spectral density of ambient CS2 have been calculated by way of\nTime Correlation Function (TCF) and instantaneous normal mode (INM)\nmethods and compared with experimental OKE data. When compared in the\nreduced Raman spectrum form, where the INM spectrum is proportional to\nthe squared polarizability derivative weighted density of states (DOS),\nthe INM results agree nearly quantitatively (at all but the lowest\nfrequencies) with the TCF results. Both are in excellent agreement with\nexperimental measurements. The INM signal has a significant contribution\nfrom the imaginary INMs. Within our INM theory of spectroscopy the\nimaginary INMs contribute like the real modes, at the magnitude of their\nimaginary frequency. When only the real modes are allowed to contribute,\nand the spectrum is rescaled to account for the missing degrees of\nfreedom, the results are much poorer, as has been observed previously.\nWhen the spectra are compared in their OKE form, the INM spectrum is\nfound to lack the low-frequency spike which is associated with long Time\nscale rotational diffusion, and it is not surprising that an INM theory\nwould not capture such a feature. The results demonstrate that while the\nOKE and spontaneous depolarized Raman spectrum contain the same\ninformation, they clearly highlight different dynamical Time scales. At\nhigher frequencies (omega > 25 cm(-1)) the INM OKE results are in\nexcellent agreement with TCF and experimental results. The TCF results\ncapture the low-frequency spike and are in agreement with experiment\neverywhere within the precision of the present calculations. The\nmolecular contributions to the OKE signal are analyzed using INM\nmethods. (C) 2000 American Institute of Physics.\n{[}S0021-9606(00)50709-0].
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A combined instantaneous normal mode and Time Correlation Function description of the infrared vibrational spectrum of ambient water
Journal of Chemical Physics, 1999Co-Authors: Heather Ahlborn, Xing Dong Ji, Brian Space, Preston MooreAbstract:A formal connection is made between the vibrational density of states (DOS) of a liquid and its approximation by way of instantaneous normal modes (INMs). This analysis leads to a quantum generalization of the INM method (QINM), and to the possibility of evaluating the classical DOS exactly. Further, INM approximations to spectroscopic quantities (e.g., infrared absorption and Raman scattering) follow in a consistent manner by evaluating the appropriate golden rule expressions for harmonic oscillators, using the INM or QINM DOS in place of the true DOS. INM and QINM methods are then applied along with traditional Time Correlation Function (TCF) methods to analyze the entire infrared (IR) spectrum of ambient water. The INM and TCF approaches are found to offer complimentary information. TCF methods are shown to offer an unexpectedly accurate description of the O-H stretching line shape. Further, the 19-fold enhancement in liquid phase absorption compared to the gas phase is also reproduced. INM and QINM methods are used to analyze the molecular origin of the water spectrum, and prove especially effective in analyzing the broad O-H stretching absorption. Further, it is argued that a motional narrowing picture is qualitatively useful in analyzing INM approximations to spectroscopy. (C) 1999 American Institute of Physics. {[}S0021-9606(99)50947-1].
