Showing papers on "Hot band published in 2022"
TL;DR: It is found that the full 282-mode model better describes the high-frequency progression of carotenoid absorption spectra; hence, vibrational modes become highly mixed during the S0 → S2 optical excitation.
Abstract: The electronic absorption spectrum of β-carotene (β-Car) is studied using quantum chemistry and quantum dynamics simulations. Vibrational normal modes were computed in optimized geometries of the electronic ground state S0 and the optically bright excited S2 state using the time-dependent density functional theory. By expressing the S2-state normal modes in terms of the ground-state modes, we find that no one-to-one correspondence between the ground- and excited-state vibrational modes exists. Using the ab initio results, we simulated the β-Car absorption spectrum with all 282 vibrational modes in a model solvent at 300 K using the time-dependent Dirac-Frenkel variational principle and are able to qualitatively reproduce the full absorption line shape. By comparing the 282-mode model with the prominent 2-mode model, widely used to interpret carotenoid experiments, we find that the full 282-mode model better describes the high-frequency progression of carotenoid absorption spectra; hence, vibrational modes become highly mixed during the S0 → S2 optical excitation. The obtained results suggest that electronic energy dissipation is mediated by numerous vibrational modes.
4 citations
TL;DR: In this article , the authors discuss the use of the "vibrational temperature" of an emitting electronic state as somewhat representative of the vibrational temperature of the gas in the discharge, and show how much all the mentioned parameters can drive to incorrect deductions from an anyway conceptually wrong measurement.
Abstract: Over the years, until the present days, a persistent mistake has been found in the literature: the use of the ‘vibrational temperature’ of an emitting electronic state as somewhat representative of the vibrational temperature of the gas in the discharge. Such a temperature is determined by fitting the spectra measured by optical emission spectroscopy. Besides the misuse of the word temperature, the results of such fittings are ambiguously named ‘vibrational temperature’ and sometimes used to argue about the vibrational non-equilibrium and its variation with discharge conditions. What has this temperature to do with the vibrational excitation of the molecules’ ground state, i.e. of the large majority of gas components? It is well established that the connection between the vibrational population of the excited and the ground state exists through the excitation process, the collisional quenching, and the vibrational relaxation in the manifold of the excited state. Nevertheless, this is very often ignored in the literature. In this note, we discuss this subject with the example of the ‘vibrational temperature’ of the N2(C, v) manifold, showing how much all the mentioned parameters can drive to incorrect deductions from an anyway conceptually wrong measurement.
3 citations
TL;DR: In this article , the vibrational modes of the tetragonal Sr3Ti2O7 compound with phase I4/mmm and symmetry D4h17 were investigated using normal coordinate analysis.
Abstract: The Raman and infrared vibrational modes have been investigated by using normal coordinate analysis for the tetragonal Sr3Ti2O7 compound having phase I4/mmm and symmetry D4h17. This is the second member of the Ruddlesden–Popper series Srn+1TinO3n+1 with n = 2. With ten short-range stretching and bending force constants, the calculation of the zone-centre vibrational modes has been done. All of the vibrational modes of the Sr3Ti2O7 compound have not been observed experimentally, and the existing vibrational modes have only been partially assigned. The Wilson’s GF-Matrix Method has been used for the first time to obtain the appropriate theoretical assignments for the Raman and infrared vibrational modes for the Sr3Ti2O7 compound. The calculated vibrational modes are consistent with the available observed experimental data. For each normal mode of the Ruddlesden–Popper phase Sr3Ti2O7, the analysis of potential energy distribution has been done for the significant impact of stretching and bending force constants towards different vibrational modes.
2 citations
TL;DR: In this article , the vibrational modes of the Ruddlesden-popper phase of the tetragonal Sr_3Ti_2O_7 compound have been investigated by using normal coordinate analysis.
Abstract: The Raman and infrared vibrational modes have been investigated by using normal coordinate analysis for the tetragonal Sr_3Ti_2O_7 compound having phase I4/mmm and symmetry D_4h^17. This is the second member of the Ruddlesden–Popper series Sr_n+1Ti_nO_3n+1 with n = 2. With ten short-range stretching and bending force constants, the calculation of the zone-centre vibrational modes has been done. All of the vibrational modes of the Sr_3Ti_2O_7 compound have not been observed experimentally, and the existing vibrational modes have only been partially assigned. The Wilson’s GF-Matrix Method has been used for the first time to obtain the appropriate theoretical assignments for the Raman and infrared vibrational modes for the Sr_3Ti_2O_7 compound. The calculated vibrational modes are consistent with the available observed experimental data. For each normal mode of the Ruddlesden–Popper phase Sr_3Ti_2O_7, the analysis of potential energy distribution has been done for the significant impact of stretching and bending force constants towards different vibrational modes. Graphical abstract
2 citations
TL;DR: In this paper, the S1(1ππ*) state decay dynamics of 2-pyridone excited around the 000 band origin was investigated using femtosecond time-resolved photoelectron imaging technique.
Abstract: The S1(1ππ*) state decay dynamics of 2-pyridone excited around the 000 band origin is investigated using femtosecond time-resolved photoelectron imaging technique. At a pump wavelength of 334.0 nm, the vibrational ground state and a few low energy vibrational states covered by the bandwidth of the pump laser pulses are excited. The lifetimes of the vibrational states show strong dependence on the vibrational energy and mode. A quantum beat between two lowest energy vibrational states is also observed. This study provides quantitative information about the vibrational-state dependent lifetime of the S1 state of 2-pyridone.
1 citations
18 Nov 2022
TL;DR: Panek et al. as mentioned in this paper employed the localized-mode vibrational self-consistent field (L-VSCF) / vibrational configuration interaction approach for predicting static 2D IR spectra.
Abstract: Computational protocols for the simulation of two-dimensional infrared (2D IR) spectroscopy usually rely on vibrational exciton models, which require an empirical parametrization. Here, we present an efficient quantum-chemical protocol for predicting static 2D IR spectra that does not require any empirical parameters. For the calculation of anharmonic vibrational energy levels and transition dipole moments, we employ the localized-mode vibrational self-consistent field (L-VSCF) / vibrational configuration interaction (L-VCI) approach previous established for (linear) anharmonic theoretical vibrational spectroscopy [Panek and Jacob, ChemPhysChem 15, 3365–3377 (2014)]. We demonstrate that with an efficient expansion of the potential energy surface using anharmonic one-mode potentials and harmonic two-mode potentials, 2D IR spectra of metal carbonyl complexes and of dipeptides can be predicted reliably. We further show how the close connection between L-VCI and vibrational exciton models can be exploited to extract the parameters of such models from those calculations. This provides a novel route to the fully quantum-chemical parametrization of vibrational exciton model for predicting 2D IR spectra.
1 citations
TL;DR: In this article , the authors proposed a low computational cost method for the quantum chemistry calculation of vibrational frequencies for large molecules by calculating the vibrational frequency for only one vibrational mode each time instead of calculating the Hessian matrix to get all vibrations.
Abstract: Quantum calculation of molecular vibrational frequency is important for infrared spectrum and Raman spectrum investigation. This work proposes a low computational cost method for the quantum chemistry calculation of vibrational frequencies for large molecules. Usually, the vibrational frequency calculation of a molecule containing N atoms requires to deal with the Hessian matrix, which consists of second derivatives of the 3N-dimensional potential hypersurface, and then solve secular equations of the matrix to obtain normal vibration modes and the corresponding frequencies. Larger N indicates more computational cost. Therefore, for a limited computational hardware condition, higher level computations for large N atomic molecule’s vibrational frequencies cannot be implemented. Here we solve this problem by calculating the vibrational frequency for only one vibrational mode each time instead of calculating the Hessian matrix to get all vibrational frequencies. When only one vibrational mode is under consideration, the molecular potential hypersurface can be transformed into one dimensional curve. Hence we can calculate the curve with high level computational method, then deduce the expression of one dimensional curve by using harmonic oscillating approximation and get the vibrational frequency by fitting the curve to the expression. It should be note that this method is applied to vibrational modes whose vibrational coordinates can be completely determined by equilibrium geometry and the molecular symmetry and be independent of the molecular force constants. It requires that no other vibrational mode with the same symmetry but different frequency exists. The lower computational cost for a one-dimensional potential curve than that for 3N-dimensional potential hypersurface’s second derivatives permit us to use higher level method and larger basis set for a given computational hardware condition to get more accurate results. In this paper we take the calculation of B2 vibrational frequency of water molecule as an example to illustrate the feasibility of this method. Furthermore, we apply this method to deal with the SF6 molecule. It has 7 atoms and 70 electrons, hence there exists large amount of electronic correlation energy to calculate. MRCI is an effective method to calculate the correlation energy. But by now no MRCI result of SF6 vibrational frequencies has been reported. So here we use MRCI/6-311G* to calculate the potential curves of A1g, Eg, T2g and T2u vibrational modes separately, deduce the expressions of them, then fit the curves to the expressions, and get the vibrational frequencies at last. The results are then compared with those obtained by other theoretical methods including HF, MP2,CISD, CCSD(T) and B3LYP methods with same 6-311G* basis set. It is shown that the relative errors to experimental results of the MRCI method is least among all these methods
TL;DR: Panek et al. as discussed by the authors employed localized-mode vibrational self-consistent field (L-VSCF)/vibrational configuration interaction approach for predicting static 2D IR spectra that does not require any empirical parameters.
Abstract: Computational protocols for the simulation of two-dimensional infrared (2D IR) spectroscopy usually rely on vibrational exciton models which require an empirical parameterization. Here, we present an efficient quantum-chemical protocol for predicting static 2D IR spectra that does not require any empirical parameters. For the calculation of anharmonic vibrational energy levels and transition dipole moments, we employ the localized-mode vibrational self-consistent field (L-VSCF)/vibrational configuration interaction (L-VCI) approach previously established for (linear) anharmonic theoretical vibrational spectroscopy [P. T. Panek and C. R. Jacob, ChemPhysChem 15, 3365-3377 (2014)]. We demonstrate that with an efficient expansion of the potential energy surface using anharmonic one-mode potentials and harmonic two-mode potentials, 2D IR spectra of metal carbonyl complexes and dipeptides can be predicted reliably. We further show how the close connection between L-VCI and vibrational exciton models can be exploited to extract the parameters of such models from those calculations. This provides a novel route to the fully quantum-chemical parameterization of vibrational exciton models for predicting 2D IR spectra.
21 Sep 2022
TL;DR: The selection rules for a polyatomic molecule are almost the same as for a pure rotational transition, with one exception as discussed by the authors , where symmetry considerations based on group theory can often be used to simplify the vibrational problem considerably.
Abstract: Translational motion is rarely interesting spectroscopically, although motion of the molecule either toward or away from the propagation direction of the light causes Doppler broadening of the spectroscopic transitions in high-resolution gas-phase experiments. Vibrational spectroscopy refers to transitions between states that differ in their vibrational quantum numbers, both within the same electronic state. For a diatomic molecule, there is only one vibrational coordinate, the internuclear separation. There are two kinds of anharmonicities associated with vibration that perturb the selection rules and energy levels derived in the harmonic oscillator limit. The essential feature of a normal mode of vibration is that all atoms oscillate about their equilibrium positions with generally different amplitudes but a common frequency and phase. The selection rules for a polyatomic molecule are almost the same as for a pure rotational transition, with one exception. Symmetry considerations based on group theory can often be used to simplify the vibrational problem considerably.
01 Dec 2022
TL;DR: In this article , very high-resolution Fourier transform spectrum of methyl alcohol and its oxygen-18 substituted variant species have been recorded in the wide range of 1.6-200 µm using a precisely controlled corner cube spectrometer developed at the University of Oulu at a resolution approaching the Doppler width of the lines with excellent signal to noise (S/N) ratio.
Abstract: In this work, very high-resolution Fourier transform spectrum of methyl alcohol and its oxygen-18 substituted variant species have been recorded in the wide range of 1.6–200 µm using a precisely controlled corner cube spectrometer developed at the University of Oulu at a resolution approaching the Doppler width of the lines with excellent signal to noise (S/N) ratio. Later some of the regions have been re-recorded using the synchrotron radiation-based Bruker spectrometer at the Canadian Light Sources with extreme accuracy. The region covers the fundamental torsional band, CO stretch band, CH3-rocking band, COH-bending band, the CH3-deformation bands, the CH3-stretch bands, and numerous other fundamental, combination, and overtone bands. The density of quantum levels in these regions makes the states highly perturbed by nearby levels. Despite the congestion due to overlapping bands the high resolution and enhanced intensity allowed assignments of some difficult bands in the most congested and complicated part of the spectra as presented in this report. In this paper, the results for new transition bands connected with the in-plane CH3 rocking mode and COH-bending modes are presented. In these transitions, one quantum of torsion is involved in the upper and state and/or lower states. For the O-18 substituted methanol strong transitions to a torsionally excited rocking vibrational state originating from the ground vibrational state have been found which should be normally forbidden. These transitions gather intensity due to a strong “Fermi” type interaction with the COH-bending mode lying immediately above. To gain some insight into the problem similar regions of the spectrum for the parent species (C-12 variant) have also been revisited. Since the strong CO stretching band is downshifted due to the presence of the heavier O-18 species, the CH3-Rocking and COH-bending are rather peaceful making this work feasible. It was possible to identify many transitions which are normally forbidden without the interaction. Detail assignments have been presented in an atlas of about 3800 highly precise spectral lines for the first time. This work should be valuable for the fundamental understanding of vibrational relaxation pathways of the molecules under consideration and the study of the extreme abundances of this molecule in interstellar space. The details can be found in the text. To save journal pages majority of the supporting data had been gathered in an Appendix.
01 Jan 2022
07 Dec 2022
TL;DR: In this article , a carbon dioxide molecule model is used to study non-equilibrium CO2 emissions in the Earth's atmosphere, which takes into account 206 vibrational states of the 7 isotopologues of CO2 giving rise 545 radiation vibrational transitions consisting of about 64200 ro-vibrational lines.
Abstract: The non-equilibrium populations of excited vibrational states of the CO2 molecules in the problem of radiation transfer in infrared bands of carbon dioxide in the middle and upper atmosphere of the Earth are investigated, taking into account changes in the absorption coefficient due to the line-mixing effect. To do this, a carbon dioxide molecule model is used to study non-equilibrium CO2 emissions in the Earth's atmosphere, which takes into account 206 vibrational states of the 7 isotopologues of CO2 giving rise 545 radiation vibrational transitions consisting of about 64200 ro-vibrational lines. The line-mixing effect was taken into account only for lines belonging to the spectral range of the 15 μm CO2 band, using a correction function to the values of the radiation absorption coefficient in this band, which was calculated within framework of the strong collision model with adjusted branch coupling. It is shown that taking into account the deviation of the frequency profile of ro-vibrational transitions in the spectral range of the 15 μm CO2 band from the sum of Voigt profiles due to the phenomenon of line-mixing leads to only insignificant (less than 2%) changes both in the values of non-equilibrium populations of vibrational states of CO2 excited in the bending mode of the CO2 molecule and in the magnitude of the rate of radiative cooling of the atmosphere in the bands of CO2. The study could be useful for understanding the radiation regime in planetary atmospheres. The results of the work may be used in the development of methods for remote sensing of atmospheric parameters.
14 Dec 2022
TL;DR: Panek et al. as discussed by the authors employed the localized-mode vibrational self-consistent field (L-VSCF) / vibrational configuration interaction approach for predicting static 2D IR spectra.
Abstract: Computational protocols for the simulation of two-dimensional infrared (2D IR) spectroscopy usually rely on vibrational exciton models, which require an empirical parametrization. Here, we present an efficient quantum-chemical protocol for predicting static 2D IR spectra that does not require any empirical parameters. For the calculation of anharmonic vibrational energy levels and transition dipole moments, we employ the localized-mode vibrational self-consistent field (L-VSCF) / vibrational configuration interaction (L-VCI) approach previous established for (linear) anharmonic theoretical vibrational spectroscopy [Panek and Jacob, ChemPhysChem 15, 3365–3377 (2014)]. We demonstrate that with an efficient expansion of the potential energy surface using anharmonic one-mode potentials and harmonic two-mode potentials, 2D IR spectra of metal carbonyl complexes and of dipeptides can be predicted reliably. We further show how the close connection between L-VCI and vibrational exciton models can be exploited to extract the parameters of such models from those calculations. This provides a novel route to the fully quantum-chemical parametrization of vibrational exciton model for predicting 2D IR spectra.