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F Merkt - One of the best experts on this subject based on the ideXlab platform.
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the rotational structure of the origin band of the pulsed Field Ionization zero kinetic energy photoelectron spectra of propene h6 and propene d6
2010Co-Authors: K Vasilatou, M Schafer, F MerktAbstract:The pulsed-Field-Ionization zero-kinetic-energy photoelectron spectra of the origin band of the X + 2 A" ← X 1 A' transition of propene (C 3 H 6 ) and perdeuterated propene (C 3 D 6 ) have been recorded at high resolution, allowing for the partial resolution of the rotational structure. The analysis of the spectra in the realm of the orbital Ionization model for rigid-rotor asymmetric-top molecules enabled the determination of the adiabatic Ionization energy of propene and the rotational constants of C 3 H 6 + and C 3 D 6 + . The tunneling splittings resulting from the hindered rotation of the methyl group could not be resolved, and the analysis was therefore carried out in the C, molecular symmetry group. Angular momentum contributions of p π , d π , and d f ) character were included in the single-center expansion describing the molecular orbital out of which Ionization occurs, leading to the selection rules |ΔN| = |N + ― N"| ≤ 2 and ΔK a = K a + ― K" a = ± 1, ±2 and to photoelectron partial waves with angular momentum quantum number up to l = 3. The observation of a strong spectral feature associated with ΔK a = 0 indicates the importance of vibronic interactions.
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assignment of the first five electronic states of ar2 from the rotational fine structure of pulsed Field Ionization zero kinetic energy photoelectron spectra
2002Co-Authors: P Rupper, F MerktAbstract:The I(1/2u), I(3/2g), I(1/2g), I(3/2u), and II(1/2u) states of Ar2+ have been investigated by pulsed-Field-Ionization zero-kinetic-energy photoelectron spectroscopy following (1+1′) resonance-enhanced two-photon excitation via the 0u+ Rydberg state located below the Ar* ([3p]54s′[1/2]1)+Ar(1S0) dissociation limit of Ar2. By selecting single rotational levels of the intermediate state, the rotational structure of five of the six lowest electronic states of Ar2+ could be observed. PhotoIonization selection rules and the magnitude of the observed Ω-doubling of the rotational levels were used to derive unambiguous assignments of the electronic symmetry of the ionic states. From the analysis of the rotational structure, the equilibrium internuclear distances, the adiabatic Ionization potentials, the dissociation energies and vibrational and anharmonic constants could be determined for the I(1/2u), I(3/2g), I(1/2g), I(3/2u), and II(1/2u) states of Ar2+. A map of the rotational energy level structure of these st...
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selective Field Ionization of high rydberg states application to zero kinetic energy photoelectron spectroscopy
2001Co-Authors: U Hollenstein, R Seiler, H Schmutz, M Andrist, F MerktAbstract:Sequences of pulsed electric Fields have been designed and tested that enable a higher selectivity in the pulsed Field Ionization of high Rydberg states (n⩾100) than has so far been possible. The enhanced selectivity originates from the permutation of the parabolic quantum numbers n1 and n2 that is induced by a sufficiently rapid inversion of the electric Field polarity during a pulse sequence. A reliable procedure, based on numerical simulations of the outcome of pulse Field Ionization sequences, has been developed to detect and control changes in the parabolic quantum numbers that can occur during a pulse sequence. The procedure can be used to assess under which conditions a clean permutation of the parabolic quantum numbers can be achieved. Unwanted randomization of m, n1 and n2, which reduces the selectivity of the Field Ionization process, can be avoided by minimizing the time intervals during which the electric Field in the pulse sequence is almost zero. The high selectivity reached in the pulsed fi...
Kaichung Lau - One of the best experts on this subject based on the ideXlab platform.
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a vacuum ultraviolet laser pulsed Field Ionization photoelectron study of sulfur monoxide so and its cation so
2011Co-Authors: Chow-shing Lam, Hailing Wang, Kaichung LauAbstract:Vacuum ultraviolet (VUV) laser pulsed Field Ionization-photoelectron (PFI-PE) spectroscopy has been applied to the study of the sulfur monoxide radical (SO) prepared by using a supersonically cooled radical beam source based on the 193 nm excimer laser photodissociation of SO2. The vibronic VUV-PFI-PE bands for the photoIonization transitions SO+(X2Π1/2; v+ = 0) ← SO(X3Σ−; v = 0); and SO+(2Π3/2; v+ = 0) ← SO(X3Σ−; v = 0) have been recorded. On the basis of the semiempirical simulation of rotational branch contours observed in these PFI-PE bands, we have obtained highly precise Ionization energies (IEs) of 83 034.2 ± 1.7 cm−1 (10.2949 ± 0.0002 eV) and 83 400.4 ± 1.7 cm−1 (10.3403 ± 0.0002 eV) for the formation of SO+(X2Π1/2; v+ = 0) and SO+(2Π3/2; v+ = 0), respectively. The present VUV-PFI-PE measurement has enabled the direct determination of the spin-orbit coupling constant (A0) for SO+(X2Π1/2,3/2) to be 365.36 ± 0.12 cm−1. We have also performed high-level ab initio quantum chemical calculations at the ...
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rovibrational state selected pulsed Field Ionization photoelectron study of methyl iodide using two color infrared vacuum ultraviolet lasers
2004Co-Authors: P Wang, Xi Xing, Kaichung Lau, H K WooAbstract:The preparation of methyl iodide (CH3I) in selected rovibrational states [ν7=1 (C-H stretch); J] by infrared (IR) excitation prior to vacuum ultraviolet (VUV) photoIonization has greatly simplified the observed pulsed Field Ionization-photoelectron (PFI-PE) spectra, allowing the direct determination of the rotational constants B+(C+)=0.254±0.003 cm−1 for CH3I+(X 2E3/2;ν7+) and the Ionization energy (76 896.9±0.2 cm−1) for CH3I+(X 2E3/2;ν7+=1,J+=3/2)←CH3I(X 1A1;ν7=1,J=0). The IR-VUV-PFI-PE and IR-VUV-photoion measurements also provide relative state-to-state (ν7+=1, J+←ν7=1, J) cross sections for the photoIonization process.
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a high resolution pulsed Field Ionization photoelectron photoion coincidence study of vinyl bromide
2004Co-Authors: Ximei Qian, Kaichung LauAbstract:By employing the high-resolution pulsed Field Ionization-photoelectron (PFI-PE)-photoion coincidence method, we have examined the unimolecular dissociation reaction of energy-selected C2H3Br+ to form C2H3++Br near its threshold. The analysis of the breakdown curves for C2H3Br+ and C2H3+ yields a value of 11.9010±0.0015 eV for the 0 K dissociative photoIonization threshold or appearance energy (AE) for C2H3+ from C2H3Br. This AE(C2H3+) value, together with the Ionization energy (IE) for C2H3Br (9.8200±0.0015 eV) obtained by PFI-PE and threshold photoelectron (TPE) measurements, has allowed the determination of the 0 K dissociation energy (D0) for the C2H3+–Br bond to be 2.081±0.002 eV. The 0 K AE(C2H3+) from C2H3Br obtained in this study corresponds to ΔHf0∘(C2H3+)=1123.7±1.9 kJ/mol. Combining the latter value and the known ΔHf0∘(C2H3)=306.7±2.1 kJ/mol, we calculated a value of 8.468±0.029 eV for the IE(C2H3), which is in accord with the result obtained in the previous photoIonization efficiency study. We ...
Lars Bojer Madsen - One of the best experts on this subject based on the ideXlab platform.
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semiclassical two step model for strong Field Ionization
2016Co-Authors: N I Shvetsovshilovski, Esa Räsänen, D G Arbo, Manfred Lein, Lars Bojer Madsen, Christoph Lemell, Joachim Burgdörfer, Károly TőkésiAbstract:We present a semiclassical two-step model for strong-Field Ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential beyond perturbation theory. Within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics, the model employs the semiclassical approximation to the phase of the full quantum propagator in the exit channel. By comparison with the exact numerical solution of the time-dependent Schr\"odinger equation for strong-Field Ionization of hydrogen, we show that for suitable choices of the momentum distribution after the first tunneling step, the model yields good quantitative agreement with the full quantum simulation. The two-dimensional photoelectron momentum distributions, the energy spectra, and the angular distributions are found to be in good agreement with the corresponding quantum results. Specifically, the model quantitatively reproduces the fan-like interference patterns in the low-energy part of the two-dimensional momentum distributions as well as the modulations in the photoelectron angular distributions.
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theory of low energy photoelectrons in strong Field Ionization by laser pulses with large ellipticity
2015Co-Authors: Darko Dimitrovski, Lars Bojer MadsenAbstract:We theoretically analyze the low-energy electrons appearing in strong-Field Ionization of atomic and molecular targets by laser pulses with large ellipticity. We present the semiclassical model used to calculate the photoelectron momentum distributions and the derivations leading to a parameter introduced in a recent combined theoretical and experimental work on naphthalene [D. Dimitrovski et al., Phys. Rev. Lett. 113, 103005 (2014)]. The parameter quantifies both the possibility to observe such low-energy electrons and their relative impact in the photoelectron momentum distributions. The numerical value of this parameter is calculated for various cases of strong-Field Ionization by elliptically polarized pulses available in the literature; in addition, the possibility to detect low-energy electrons for large $\ensuremath{\epsilon}$ and different targets, including simple atoms, is discussed.
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low energy photoelectrons in strong Field Ionization by laser pulses with large ellipticity
2014Co-Authors: Darko Dimitrovski, Henrik Stapelfeldt, Jochen Maurer, Lars Bojer MadsenAbstract:The 3D photoelectron momentum distributions created by the strong-Field Ionization of argon atoms and naphthalene molecules with intense, large ellipticity ($\ensuremath{\sim}0.7$) femtosecond laser pulses are studied. The experiment reveals the presence of low-energy electrons for randomly oriented naphthalene, but not for argon. Our theory shows that the induced dipole part of the cationic potential facilitates the creation of the low-energy electrons. We establish the conditions in terms of laser pulse parameters and molecular properties for which this type of low-energy electrons can be observed and point to applications thereof.
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Strong-Field Ionization of diatomic molecules and companion atoms: Strong-Field approximation and tunneling theory including nuclear motion
2005Co-Authors: Thomas Kim Kjeldsen, Lars Bojer MadsenAbstract:We present a detailed comparison of strong-Field Ionization of diatomic molecules and their companion atoms with nearly equal Ionization potentials. We perform calculations in the length and velocity gauge formulations of the molecular strong-Field approximation and with the molecular tunneling theory, and in both cases we consider effects of nuclear motion. A comparison of our results with experimental data shows that the length gauge strong-Field approximation gives the most reliable predictions.
Frederic Merkt - One of the best experts on this subject based on the ideXlab platform.
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high resolution pulsed Field Ionization zero kinetic energy photoelectron spectroscopic study of the two lowest electronic states of the ozone cation o3
2005Co-Authors: Stefan Willitsch, Fabrizio Innocenti, John M Dyke, Frederic MerktAbstract:The pulsed-Field-Ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectrum of jet-cooled O-3 has been recorded in the range 101 000-104 000 cm(-1). The origins of the X (1)A(1)-->X+ (2)A(1) and X (1)A(1)-->A(+) B-2(2) transitions could be determined from the rotational structure of the bands, the photoIonization selection rules, the photoIonization efficiency curve, and comparison with ab initio calculations. The first adiabatic Ionization energy of O-3 was measured to be 101 020.5(5) cm(-1) [12.524 95(6) eV] and the energy difference between the X+ (2)A(1) (0,0,0) and A(+) B-2(2) (0,0,0) states was determined to be DeltaT(0)=1089.7(4) cm(-1). Whereas the X-->X+ band consists of an intense and regular progression in the bending (nu(2)) mode observed up to v(2)(+)=4, only the origin of the X-->A(+) band was observed. The analysis of the rotational structure in each band led to the derivation of the r(0) structure of O-3(+) in the X+ [C-2v,r(0)=1.25(2) A,alpha(0)=131.5(9)degrees] and A(+)[C-2v,r(0)=1.37(5) A,alpha(0)=111.3(38)degrees] states. The appearance of the spectrum, which is regular up to 102 300 cm(-1), changes abruptly at approximate to102 500 cm(-1), a position above which the spectral density increases markedly and the rotational structure of the bands collapses. On the basis of ab initio calculations, this behavior is attributed to the onset of large-amplitude motions spreading through several local minima all the way to large internuclear distances. The ab initio calculations are consistent with earlier results in predicting a seam of conical intersections between the X+ and A(+) states approximate to2600 cm(-1) above the cationic ground state and demonstrate the existence of potential minima at large internuclear distances that are connected to the main minima of the X+ and A(+) states through low-lying barriers.
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collisional and electric Field effects in the delayed pulsed Field Ionization zero kinetic energy photoelectron spectrum of argon
1994Co-Authors: Frederic MerktAbstract:The pulsed Field Ionization (PFI) zero‐kinetic‐energy (ZEKE) photoelectron spectrum of argon has been recorded in the region of the transition from the ground neutral state (1S0) to the first two Ionization limits corresponding to the two spin–orbit levels (2P3/2 and 2P1/2) of the ground state of the ion. The high‐n Rydberg states (85
Bernhard H Schlegel - One of the best experts on this subject based on the ideXlab platform.
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effect of spin orbit coupling on strong Field Ionization simulated with time dependent configuration interaction
2020Co-Authors: Mi Kyung Lee, Paul Hoerner, Bernhard H SchlegelAbstract:Time-dependent configuration interaction with a complex absorbing potential has been used to simulate strong Field Ionization by intense laser Fields. Because spin-orbit coupling changes the energies of the ground and excited states, it can affect the strong Field Ionization rate for molecules containing heavy atoms. Configuration interaction with single excitations (CIS) has been employed for strong Field Ionization of closed shell systems. Single and double excitation configuration interaction with Ionization (CISD-IP) has been used to treat Ionization of degenerate states of cations on an equal footing. The CISD-IP wavefunction consists of ionizing single (one hole) and double (two hole/one particle) excitations from the neutral atom. Spin-orbit coupling has been implemented using an effective one electron spin-orbit coupling operator. The effective nuclear charge in the spin-orbit coupling operator has been optimized for Ar+, Kr+, Xe+, HX+ (X = Cl, Br, and I). Spin-orbit effects on angular dependence of the strong Field Ionization have been studied for HX and HX+. The effects of spin-orbit coupling are largest for Ionization from the π orbitals of HX+. In a static Field, oscillations are seen between the 2Π3/2 and 2Π1/2 states of HX+. For Ionization of HX+ by a two cycle circularly polarized pulse, a single peak is seen when the maximum in the carrier envelope is perpendicular to the molecular axis and two peaks are seen when it is parallel to the axis. This is the result of the greater Ionization rate for the π orbitals than for the σ orbitals.
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angular dependence of strong Field Ionization of n2 by time dependent configuration interaction using density functional theory and the tamm dancoff approximation
2019Co-Authors: Paul Hoerner, Mi Kyung Lee, Bernhard H SchlegelAbstract:The Ionization of N2 serves as an important test case for computational methods for strong Field Ionization. Because Koopmans’s theorem fails for Hartree-Fock calculations of N2, corrections for electron correlation are needed to obtain the proper ordering of Ionization energies of N2. Lopata and co-workers found that real-time integration of time-dependent Hartree-Fock (rt-TD-HF) gave a ratio for strong Field Ionization parallel and perpendicular to the molecular axis that was too small compared to experiment, but real-time integration of time-dependent density functional theory (rt-TD-DFT) with an appropriately tuned long-range corrected functional, lc-ωPBE*, was in good agreement with experiment. The present study finds that time-dependent configuration interaction (TDCI) with single excitations based on a Hartree-Fock reference determinant (TD-CIS) has the same problems as rt-TD-HF. These problems can be overcome within the TDCI framework by calculating the excitation energies and transition dipole moments with density functional theory using linear response TD-DFT in the Tamm-Dancoff approximation (TDA) with suitably tuned long-range corrected functionals (TD-TDA). The correct angular dependence of the total Ionization rate is obtained with TD-TDA using tuned lc-ωPBE*, lc-BLYP*, and ωB97XD* functionals. Partitioning of the total Ionization rate into orbital components confirms that the larger Ionization rate perpendicular to the molecular axis found for TD-CIS is due to greater π orbital contributions than those seen in TD-TDA. The use of density functional theory corrects this problem. At higher Fields, both the TD-CIS and TD-TDA simulations show an increased Ionization rate perpendicular to the molecular axis because of increased Ionization from the π orbitals.The Ionization of N2 serves as an important test case for computational methods for strong Field Ionization. Because Koopmans’s theorem fails for Hartree-Fock calculations of N2, corrections for electron correlation are needed to obtain the proper ordering of Ionization energies of N2. Lopata and co-workers found that real-time integration of time-dependent Hartree-Fock (rt-TD-HF) gave a ratio for strong Field Ionization parallel and perpendicular to the molecular axis that was too small compared to experiment, but real-time integration of time-dependent density functional theory (rt-TD-DFT) with an appropriately tuned long-range corrected functional, lc-ωPBE*, was in good agreement with experiment. The present study finds that time-dependent configuration interaction (TDCI) with single excitations based on a Hartree-Fock reference determinant (TD-CIS) has the same problems as rt-TD-HF. These pr...
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angular dependence of strong Field Ionization of haloacetylenes hccx x f cl br i using time dependent configuration interaction with an absorbing potential
2018Co-Authors: Paul Hoerner, Bernhard H SchlegelAbstract:Strong Field Ionization of haloacetylenes was simulated by time-dependent configuration interaction using all single excitations and a complex absorbing potential. The angular dependence of Ionization for HCCX was mapped with static electric Fields in the range 0.01–0.06 atomic units and compared with the results for CH3X. HCCF ionizes primarily from the CC π orbital. HCCX (X = Cl, Br, I) compounds show increasing amounts of Ionization from the halogen π-type lone pair orbitals and have a node perpendicular to the molecular axis. These shapes can be understood in terms of the energies and interactions of the halogen π-type lone pairs with the π orbitals of the CC triple bond.
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strong Field Ionization rates of linear polyenes simulated with time dependent configuration interaction with an absorbing potential
2014Co-Authors: Pascal Krause, Bernhard H SchlegelAbstract:The strong Field Ionization rates for ethylene, trans 1,3-butadiene, and trans,trans 1,3,5-hexatriene have been calculated using time-dependent configuration interaction with single excitations and a complex absorbing potential (TDCIS-CAP). The calculations used the aug-cc-pVTZ basis set with a large set of diffuse functions (3 s, 2 p, 3 d, and 1 f) on each atom. The absorbing boundary was placed 3.5 times the van der Waals radius from each atom. The simulations employed a seven-cycle cosine squared pulse with a wavelength of 800 nm. Ionization rates were calculated for intensities ranging from 0.3 × 1014 W/cm2 to 3.5 × 1014 W/cm2. Ionization rates along the molecular axis increased markedly with increasing conjugation length. By contrast, Ionization rates perpendicular to the molecular axis were almost independent of the conjugation length.