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V A Apkarian - One of the best experts on this subject based on the ideXlab platform.
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surface enhanced raman trajectories on a nano dumbbell transition from field to charge transfer plasmons as the spheres fuse
ACS Nano, 2012Co-Authors: Mayukh Banik, Patrick Z Elkhoury, Amit Nag, Alejandro Rodriguezperez, Nekane Guarrottxena, Guillermo C Bazan, V A ApkarianAbstract:By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The Linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic Spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced Spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from Line Spectra to band Spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, w...
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surface enhanced raman trajectories on a nano dumbbell transition from field to charge transfer plasmons as the spheres fuse
ACS Nano, 2012Co-Authors: Mayukh Banik, Patrick Z Elkhoury, Amit Nag, Alejandro Rodriguezperez, Nekane Guarrottxena, Guillermo C Bazan, V A ApkarianAbstract:By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The Linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic Spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced Spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from Line Spectra to band Spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, which evolves at a speed of ∼1 A/min. The crossover to the conduction limit is marked by the transition of Line Spectra to Stark-broadened and shifted band Spectra. As the junction closes on CO, the local field reaches 1 V/A, limited to a current of 1 electron per vibrational cycle passing through the molecule, with associated Raman enhancement factor via the charge transfer plasmon resonance of 10(12). The local field identifies that a sharp protrusion is responsible for room-temperature chemisorption of CO on silver. The asymmetric phototunneling junction, Ag-CO-Ag, driven by the frequency-tunable charge transfer plasmon of the dumbbell antenna, combines the design elements of an ideal rectifying photocollector.
Gemma Busquet - One of the best experts on this subject based on the ideXlab platform.
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far infrared Line Spectra of seyfert galaxies from the herschel pacs spectrometer
The Astrophysical Journal, 2015Co-Authors: L Spinoglio, M Pereirasantaella, Matthew A Malkan, K M Dasyra, L Calzoletti, Silvia Tommasin, Gemma BusquetAbstract:We observed the far-IR fine-structure Lines of 26 Seyfert galaxies with the Herschel-PACS spectrometer. These observations are complemented with Spitzer Infrared Spectrograph and Herschel SPIRE spectroscopy. We used the ionic Lines to determine electron densities in the ionized gas and the [C I] Lines, observed with SPIRE, to measure the neutral gas densities, while the [O I] Lines measure the gas temperature, at densities below ~104 cm–3. Using the [O I]145 μm/63 μm and [S III]33/18 μm Line ratios, we find an anti-correlation of the temperature with the gas density. Various fine-structure Line ratios show density stratifications in these active galaxies. On average, electron densities increase with the ionization potential of the ions. The infrared Lines arise partly in the narrow Line region, photoionized by the active galactic nucleus (AGN), partly in H II regions photoionized by hot stars, and partly in photo-dissociated regions. We attempt to separate the contributions to the Line emission produced in these different regions by comparing our observed emission Line ratios to theoretical values. In particular, we tried to separate the contribution of AGNs and star formation by using a combination of Spitzer and Herschel Lines, and we found that besides the well-known mid-IR Line ratios, the Line ratio of [O III]88 μm/[O IV]26 μm can reliably discriminate the two emission regions, while the far-IR Line ratio of [C II]157 μm/[O I]63 μm is only able to mildly separate the two regimes. By comparing the observed [C II]157 μm/[N II]205 μm ratio with photoionization models, we also found that most of the [C II] emission in the galaxies we examined is due to photodissociation regions.
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far infrared Line Spectra of seyfert galaxies from the herschel pacs spectrometer
arXiv: Astrophysics of Galaxies, 2014Co-Authors: L Spinoglio, M Pereirasantaella, Matthew A Malkan, K M Dasyra, L Calzoletti, Silvia Tommasin, Gemma BusquetAbstract:We present spectroscopic observations of FIR fine-structure Lines of 26 Seyfert galaxies obtained with the Herschel-PACS spectrometer. These observations are complemented by spectroscopy with Spitzer-IRS and Herschel-SPIRE. The ratios of the OIII, NII, SIII and NeV Lines have been used to determine electron densities in the ionised gas regions. The CI Lines, observed with SPIRE, have been used to measure the densities in the neutral gas, while the OI Lines provide a measure of the gas temperature, at densities below 10000 cm-3. Using the OI145/63um and SIII33/18um Line ratios we find an anti-correlation of the temperature with the gas density. Using various fine-structure Line ratios, we find that density stratification is common in these active galaxies. On average, the electron densities increase with the ionisation potential of the ions producing the NII, SIII and NeV emission. The infrared emission Lines arise partly in the Narrow Line Region (NLR) photoionised by the AGN central engine, partly in HII regions photo ionised by hot stars and partly in neutral gas in photo-dissociated regions (PDRs). We attempt to separate the contributions to the Line emission produced in these different regions by comparing our emission Line ratios to empirical and theoretical values. In particular, we tried to separate the contribution of AGN and star formation by using a combination of Spitzer and Herschel Lines, and we found that, besides the well known mid-IR Line ratios, the mixed mid-IR/far-IR Line ratio of OIII88um/OIV26um can reliably discriminate the two emission regimes, while the far-IR Line ratio of CII157um/OI63um is only able to mildly separate the two regimes. By comparing the observed CII157um/NII205um ratio with photoionisation models, we also found that most of the CII emission in the galaxies we examined is due to PDRs.
Mayukh Banik - One of the best experts on this subject based on the ideXlab platform.
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surface enhanced raman trajectories on a nano dumbbell transition from field to charge transfer plasmons as the spheres fuse
ACS Nano, 2012Co-Authors: Mayukh Banik, Patrick Z Elkhoury, Amit Nag, Alejandro Rodriguezperez, Nekane Guarrottxena, Guillermo C Bazan, V A ApkarianAbstract:By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The Linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic Spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced Spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from Line Spectra to band Spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, w...
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surface enhanced raman trajectories on a nano dumbbell transition from field to charge transfer plasmons as the spheres fuse
ACS Nano, 2012Co-Authors: Mayukh Banik, Patrick Z Elkhoury, Amit Nag, Alejandro Rodriguezperez, Nekane Guarrottxena, Guillermo C Bazan, V A ApkarianAbstract:By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The Linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic Spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced Spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from Line Spectra to band Spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, which evolves at a speed of ∼1 A/min. The crossover to the conduction limit is marked by the transition of Line Spectra to Stark-broadened and shifted band Spectra. As the junction closes on CO, the local field reaches 1 V/A, limited to a current of 1 electron per vibrational cycle passing through the molecule, with associated Raman enhancement factor via the charge transfer plasmon resonance of 10(12). The local field identifies that a sharp protrusion is responsible for room-temperature chemisorption of CO on silver. The asymmetric phototunneling junction, Ag-CO-Ag, driven by the frequency-tunable charge transfer plasmon of the dumbbell antenna, combines the design elements of an ideal rectifying photocollector.
S Kurtz - One of the best experts on this subject based on the ideXlab platform.
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the early evolution of massive stars radio recombination Line Spectra
The Astrophysical Journal, 2008Co-Authors: Eric Keto, Qizhou Zhang, S KurtzAbstract:Velocity shifts and differential broadening of radio recombination Lines are used to estimate the densities and velocitiesof theionizedgasinseveralhypercompactandultracompactHiiregions.ThesesmallHiiregionsarethought tobeattheirearliestevolutionaryphaseandassociatedwiththeyoungestmassivestars.Theobservationssuggestthat these H ii regions are characterized by high densities, supersonic flows, and steep density gradients, consistent with accretion and outflows that would be associated with the formation of massive stars. Subject headingg: H ii regions — stars: early-type — stars: formation
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the early evolution of massive stars radio recombination Line Spectra
arXiv: Astrophysics, 2007Co-Authors: Eric Keto, Qizhou Zhang, S KurtzAbstract:Velocity shifts and differential broadening of radio recombination Lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact HII regions. These small HII regions are thought to be at their earliest evolutionary phase and associated with the youngest massive stars. The observations suggest that these HII regions are characterized by high densities, supersonic flows and steep density gradients, consistent with accretion and outflows that would be associated with the formation of massive stars.
A Humphrey - One of the best experts on this subject based on the ideXlab platform.
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deep spectroscopy of the fuv optical emission Lines from a sample of radio galaxies at z 2 5 metallicity and ionization
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: A Humphrey, M Villarmartin, J Vernet, R A E Fosbury, S Di Serego Alighieri, L BinetteAbstract:We present long-slit near-infrared (NIR) Spectra, obtained using the Infrared Spectrometer And Array Camera (ISAAC) instrument at the Very Large Telescope, which sample the rest-frame optical emission Lines from nine radio galaxies at z∼ 2.5. One-dimensional Spectra have been extracted and, using broad-band photometry, have been cross-calibrated with Spectra from the literature to produce Line Spectra spanning a rest wavelength of ∼1200–7000 A. The resulting Line Spectra have a Spectral coverage that is unprecedented for radio galaxies at any redshift. We have also produced a composite of the rest-frame ultraviolet (UV)–optical Line fluxes of powerful, z∼ 2.5 radio galaxies. We have investigated the relative strengths of Lyα, Hβ, Hα, He iiλ1640 and He iiλ4687, and we find that Av can vary significantly from object to object. In addition, we have identified new Line ratios to calculate electron temperature: [Ne v]λ1575/[Ne v]λ3426, [Ne iv]λ1602/[Ne iv]λ2423, O iii]λ1663/[O iii]λ5008 and [O ii]λ2471/[O ii]λ3728. We calculate an average O iii temperature of 14100+1000−600 K. We have modelled the rich emission Line Spectra, and we conclude that they are best explained by active galactic nucleus (AGN) photoionization with the ionization parameter U varying between objects. For shock models (with or without the precursor) to provide a satisfactory explanation for the data, an additional source of ionizing photons is required – presumably the ionizing radiation field of the AGN. Single slab photoionization models are unable to reproduce the high- and the low-ionization Lines simultaneously: the higher ionization Lines imply higher U than do the lower ionization Lines. This problem may be alleviated either by combining two or more single slab photoionization models with different U, or by using mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann. In either case, U must vary from object to object. On the basis of N v/N iv] and N iv]/C iv we argue that, while photoionization is the dominant ionization mechanism in the extended emission Line regions (EELR), shocks make a fractional contribution (∼10 per cent) to its ionization. The N v/N iv] and N iv]/C iv ratios in the broad-Line region (BLR) of some quasars suggest that shock ionization may be important in the BLR also. We find that in the EELR of z∼ 2 radio galaxies the N/H abundance ratio is close to its solar value. We conclude that N/H and metallicity do not vary by more than a factor of 2 in our sample. These results are consistent with the idea that the massive ellipticals which become the hosts to powerful AGN are assembled very early in the history of the universe, and then evolve relatively passively up to the present day.
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deep spectroscopy of the fuv optical emission Lines from a sample of radio galaxies at z 2 5 metallicity and ionization
arXiv: Astrophysics, 2007Co-Authors: A Humphrey, M Villarmartin, J Vernet, R A E Fosbury, S Di Serego Alighieri, L BinetteAbstract:We present long-slit NIR Spectra, obtained using the ISAAC instrument at the Very Large Telescope, for nine radio galaxies at z~2.5. One-dimensional Spectra have been extracted and cross calibrated with optical Spectra from the literature to produce Line Spectra spanning a rest wavelength of ~1200-7000 A. We have also produced a composite of the rest-frame UV-optical Line fluxes of powerful, z~2.5 radio galaxies. We have investigated the relative strengths of Ly-alpha, H-beta, H-alpha, HeII 1640 and HeII 4687, and we find that Av can vary significantly from object to object. In addition, we identify new Line ratios to calculate electron temperature: [NeV] 1575/[NeV] 3426, [NeIV] 1602/[NeIV] 2423, OIII] 1663/[OIII] 5008 and [OII] 2471/[OII]3728. We model the emission Line Spectra and conclude they are best explained by AGN-photoionization with the ionization parameter U varying between objects. Single slab photoionization models are unable to reproduce the high- and the low-ionization Lines simultaneously: this may be alleviated either by combining two or more single slab photoionization models with different U, or by using mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann (1996). On the basis of NV/NIV] and NIV]/CIV we argue that shocks make a fractional contribution to the ionization of the EELR. We find that in the EELR of z~2 radio galaxies the N/H abundance ratio is close to its solar value. We conclude that N/H and metallicity do not vary by more than a factor of two in our sample. This is consistent with the idea that massive ellipticals are assembled very early in the history of the universe, and then evolve relatively passively up to the present day.