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Cu2ZnSn(S,Se)4 (CZT(S,Se)) thin films exhibit the characteristics necessary to be effective absorbers in solar cells. In this report, the room temperature experimental Raman scattering spectra, recorded at different excitation wavelengths, are systematically analyzed theoretically using the results of DFT harmonic frequencies calculations at the Γ-point for various modifications of kesterite (KS), stannite (ST), and pre-mixed Cu-Au (PMCA) crystal structures. The specific anharmonism‐induced features in the spectra of CZT(S,Se) crystals are identified, and the spectral lineshapes at varied strengths of anharmonic interaction are simulated. A robust agreement between the experimental Raman spectrum and the theoretical results is demonstrated, ensuring the reliability of estimating parameters related to anharmonic effects. Therefore, our findings show that incorporating anharmonism as an additional contribution to the phonon spectra, particularly in non-resonant cases, allows for a more accurate description of the vibrational properties of CZT(S,Se). This could play a crucial role in distinguishing between different phases of CZT(S,Se) materials and open new possibilities for the fabrication of solar cells with enhanced characteristics. [ABSTRACT FROM AUTHOR]

The Raman spectra in the C-H stretching region are of great importance for the study of the structure and dynamics of organic compounds. However, the Fermi resonance between the first overtone mode of C-H bending vibration and C-H stretching vibration typically results in the disturbance of Raman bands in the C-H stretching region. In this context, a specific deuterated molecule with only one C–H bond was proposed, and it was found that the frequency of the first overtone mode of the C-H bending vibration was significantly different from the frequency of the C-H stretching vibration. Due to the significant discrepancy, Fermi resonance in the C-H stretching region was eliminated from the experimental and theoretical Raman spectra of deuterated leucine, deuterated benzoin, deuterated methanol, and deuterated ethanol. Hence then, the Raman spectra of these specific deuterated compounds in the C-H stretching region can be used to study the structure or the dynamics of the organic compounds. [ABSTRACT FROM AUTHOR]

Studying the vibrational energy flow within molecules can help us better understand their reactivity and facilitate the design of novel functional groups for potential drug candidates. This study examined the conformation of benzene sulfonamide in solvents and vacuum. Potential energy surfaces were computed for the two possible conformations, showing that the conformers' stability varied with the medium. Additionally, the vibrational energy redistribution of halogen‐substituted benzene sulfonamide conformers was studied in solvents and vacuums. The lifetimes of the halogen stretching mode C−X (where X=F, Cl, or Br) in the substituted benzene sulfonamides were calculated and compared. The solvent and vacuum media lifetimes followed the order: C−Cl>C−Br>C−F. However, the degree of delocalization of vibrational energy was found to vary between them. [ABSTRACT FROM AUTHOR]

The IR transmittance spectrum of an isotopic mixture of chlorodifluoromethane (CHF2Cl, Ereon-22) with a 33% fraction of 13C and a natural ratio of chlorine isotopes was measured in the frequency range 1400–740 cm–1 with a resolution of 0.001 cm–1 at a temperature of 20°C. An ab initio calculation of the structure and sextic potential energy surface and surfaces of the components of the dipole moment has been carried out by the electronic quantum-mechanical method of Moller–Plesset, MP2/cc-pVTZ. Then the potential was optimized by replacing the harmonic frequencies with the frequencies calculated by the electronic method of coupled clusters, CCSD(T)/aug-cc-pVQZ. The fundamental and combination frequencies were calculated using the operator perturbation theory of Van Vleck (CVPTn) of the second and fourth order (n = 2, 4). Resonance effects were modeled using an additional variational calculation in the basis up to fourfold VCI excitation (4). The average prediction error for the fundamental frequencies of the 12C isotopologues was ~1.5 cm–1. The achieved accuracy made it possible to reliably predict the isotopic frequency shifts of the 13C isotopologues. It is shown that the strong Fermi resonance ν4/2ν6 dominates in the 12C isotopologues and is practically absent in 13C. The literature assumption [Spectrochim. Acta A, 44:553] about the splitting of ν1(CH) due to the resonance ν1/ν2 + ν7 + ν9 is confirmed. The coefficients of the polyadic quantum number are determined. The analysis made it possible to carry out a preliminary identification of the centers of the vibrational-rotational bands of isotopologues 13CHF235Cl and 13CHF237Cl in the spectrum of the mixture in preparation for individual analyzes of the vibrational-rotational structures of individual vibrational transitions. [ABSTRACT FROM AUTHOR]

The radiative forcing (RF) of climate change due to increases in carbon dioxide (CO2) concentration is primarily in the wavenumber region 500–850 cm−1 (wavelengths of approximately 12 to 20 μm). It originates from absorption and emission of infrared radiation due to vibrational–rotational transitions of the CO2 molecule. While this RF has been the subject of intense and detailed study, to date, the contribution of different vibrational transitions to this forcing has not been explored. This article presents an analysis of radiative transfer calculations that quantify the role of different vibrational transitions and illustrates that while the fundamental bending mode contributes nearly 90% of the total infrared intensity, it contributes less than half of the RF at present‐day CO2 concentrations; this is because the absorption at the centre of this fundamental band is so intense that the effect of additional CO2 is strongly muted. By successively adding in additional CO2 bands to the calculations, it is demonstrated that a key spectroscopic phenomenon, known as Fermi Resonance (an interaction between excited states of the bending and the symmetric stretching modes of CO2) leads to a significant spreading of the infrared intensity to both higher and lower wavenumbers, where the fundamental bending mode is less important. The Fermi Resonance transitions contribute only about 4% of the total infrared intensity in this spectral region but cause more than half of the present‐day RF. The less‐abundant isotopologues of CO2 have little impact on the spectrally integrated RF, but this small contribution results from a compensation between more significant positive and negative contributions to the spectral RF. This work does not alter the results of detailed RF calculations available in the literature; rather, it helps explain the physical basis of that forcing. [ABSTRACT FROM AUTHOR]

In situ high‐pressure Raman spectroscopy experiments have been performed to investigate the structural changes of parabanic acid (PA) up to ~12.0 GPa. The analysis of Raman spectroscopy reveals that PA undergoes two phase transitions. The collapse of spacing between molecular layers and the distortion of hydrogen‐bonding networks almost in ac‐plane are the main causes of the first phase transition above 2.1 GPa. The changes of Fermi resonance parameters also provide evidence for the first phase transitions. The second phase transition around 4.0 GPa can attribute to the further reduction of the molecular interlayer spacing and the resulting distortion of hydrogen‐bonding network. First‐principle calculations and Hirshfeld surfaces further confirm the analysis of the experimental results. The analysis of high‐pressure phase transition contributes a better explanation for the high‐pressure phase transition process of layered supramolecular materials with hydrogen‐bond self‐assembly. This study provides the possibility of two new polymorphs for PA under high pressure and is helpful for broadening its potential application of this material, especially in the field of supramolecular chemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-pressure Raman spectra of xylitol from atmospheric pressure to 9.08 GPa. • An anharmonic coupling between peaks of fundamental modes of xylitol at 2945 cm−1 and 2955 cm−1 at 0.99 GPa. • The influence of pressure on hydrogen bonding in xylitol molecules. Xylitol, as a typical polyol, has a broad range of application prospects. However, the molecular states of xylitol under different environments are rarely reported until now. In this work, the state changes of xylitol molecules under high pressure were analyzed by Raman spectra. A Fermi resonance phenomenon in the fundamental mode of xylitol at 2945 (±0.06) cm−1 and 2955 (±0.41) cm−1 was observed at 0.99 GPa. The Fermi doublets possess the same symmetry and close energy levels, which had not been changed by pressures. However, the high pressure shortened the atomic distances and applied the extra disturbance, providing the necessary conditions for energy transfer. Besides, the Fermi doublets decoupling happened at 4 GPa due to the breaking of hydrogen bonding. This work provides an important reference for studying molecular states and weak interactions of polyols under high pressures. [ABSTRACT FROM AUTHOR]

In this work, the structural dynamics of the chloromethanes CCl4, CHCl3 and CH2Cl2 were evaluated through a computational spectroscopy approach by comparing experimental inelastic neutron scattering (INS) spectra with the corresponding simulated spectra obtained from periodic DFT calculations. The overall excellent agreement between experimental and calculated spectra allows a confident assignment of the vibrational features, including not only the molecular fundamental modes but also lattice and combination modes. In particular, an impressive overtone sequence for CHCl3 is fully described by the simulated INS spectrum. In the CCl4 spectrum, the splitting of the ν3 mode at ca. 765–790 cm−1 is discussed on the basis of the Fermi resonance vs. crystal splitting controversy. [ABSTRACT FROM AUTHOR]

The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method. The reaction dynamics are studied for the reactant CH3D initially from the ground state, the CH3 symmetry and asymmetry stretching excitation, the CD stretching excitation and the fundamental and the first overtone of the CH3 bending mode. The calculated reaction probabilities show that exciting either of the CH3 stretching modes enhances the reactivity in the collision energy range below 1.0 eV, while the CD stretching excitation does not obviously prompt the reaction. Fundamental CH3 bending excitation has nearly no effect on promoting reactivity. However, a significant enhancement is observed for the first overtone excitation of the CH3 bending mode, resulting from the Fermi resonance between the fundamental state of the CH3 symmetry stretching mode and the first overtone state of the CH3 bending mode. [ABSTRACT FROM AUTHOR]

Vibrational spectra of the methyl groups in CH3SH, CH3SCH3, CH3OH, and CH3OCH3 monomers were measured to analyze their complex features as a result of bend/umbrella‐stretch Fermi resonance. Multiple bands were recorded between 2800–3000 cm−1 associated with the vibrations of the methyl groups in CH3OH, and CH3OCH3. On the other hand, the corresponding spectra of CH3SH and CH3SCH3 are relatively simpler with main peaks between 2900 to 3000 cm−1. Theoretical ab initio anharmonic algorithm using six normal modes on a methyl group with potential energy surface at CCSD(T)‐F12/aug‐cc‐pVTZ quality is able to account for all the experimentally observed features across these four species. In CH3SCH3 and CH3SH, all three CH stretch fundamentals are above 2900 cm−1, but the fundamental of umbrella mode is lower than 1350 cm−1, thus only the overtone states of two bending modes are able to borrow sufficient intensities. In CH3OCH3 and CH3OH, umbrella modes have frequencies similar to the bending modes and the CH stretch fundamentals are red‐shifted to 2850–2950 cm−1 leading to more complex vibrational features due to better energy‐matching condition. [ABSTRACT FROM AUTHOR]

• The effect of H-Bond on the FR in the Py-Water was performed via DFT method. • At the pyridine mole fraction of 0.7, water preferentially affinity to the pyridine molecule, and the Fermi doublet changes obviously. • At the pyridine mole fraction of 0.5, the structure of the H-Bond network is most favorable for the bonding of Py molecules. The Fermi resonance (FR) occurs between the ring breathing vibrational (ν 1) and the triangular stretching (ν 12) mode of pyridine in aqueous pyridine solution was studied using Raman spectroscopy combined with density functional theory (DFT) calculations. The effect of H-Bond on the FR in the mixture was performed by MD analysis. Combined with the FR parameters, it was found that due to the H-Bond effect the FR coupling changed significantly when the pyridine mole fractions were near 0.7 and 0.5, respectively. The water H-Bond network structure is most favorable for pyridine molecule bonding at a pyridine mole concentration around 0.5, and water preferentially affinity to the pyridine molecule at x = 0.7. In addition, we analyzed the O H vibrational region at different mole fractions and theoretically calculated Py associated O H in specific molecular bonds. [Display omitted] [ABSTRACT FROM AUTHOR]

• Investigating the impact of methanol(CH 3 OH) hydrogen bonding network on the Fermi resonance of acetonitrile(CH 3 CN). • Analyze the changes of hydrogen bonding network in CH 3 CN-CH 3 OH binary solution by Raman spectroscopy. • Using density functional theory (DFT) and reduced density gradient (RDG) to analyze the hydrogen bonding network in acetonitrile-methanol solutions of different concentrations. Fermi resonance (FR) is a molecular vibrational coupling and energy transfer phenomenon existing within or between molecules. Raman spectra of acetonitrile-methanol (CH 3 CN-CH 3 OH) solutions were measured with different volume fractions, and the FR effect between nitrile stretching mode (ν 2) and the combination modes (ν 3 + ν 4) in acetonitrile was obtained. The Fermi doublets of ν 2 ∼ ν 3 + ν 4 exhibit a blue-shift as the concentration of CH 3 CN decreases. The calculated FR parameters indicate that the hydrogen bonding (HB) network between CH 3 CN and CH 3 OH molecules represents a linear modulation effect on the FR. Meanwhile, we also investigated the O–H stretching region of CH 3 OH and utilized Density Functional Theory (DFT) and reduced density gradient (RDG) analysis to reveal the changes in the HB network of CH 3 OH. The result strongly implies a robust correlation between the O–H band and the FR. The results are of significance for understanding influence of HB on FR effect in binary solutions and for further studying the modulatory role of organic solvents on the FR effect of CH 3 CN. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four frequencies have been observed in the VV and VH component Raman spectra of VC. • Established the model for the conjunction of intramolecular and intermolecular vibrational coupling. • Proposed the Schrödinger equation and obtained four energy solutions for the antiparallel alignment mode. • Intramolecular and intermolecular interaction constants have been determined individually at different concentration. • Dimer structure and DFT calculations can reproduce the NCE and concentration effects. The positions of splitting bands resulting from simultaneous intramolecular (such as Fermi resonance) and intermolecular interactions were calculated by a variational method. Hamiltonian calculation model employed an antiparallel arrangement. Four nondegenerate energy solutions were obtained, which correspond exactly to the four peaks observed in polarized Raman spectroscopy and high resolution infrared spectroscopy: two in the VV component and two in the VH component. The intramolecular coupling constant W, unperturbed intensity ratios R, and unperturbed band difference X 0 for vinylene carbonate (VC) were calculated from the derived equations and the experimental data at infinite dilution concentration. Additionally, the intermolecular interaction constants V of VC in different polar solvents (VC/CH 3 CN, VC/CHCl 3 and VC/CH 3 OH binary mixtures) at varying concentrations were calculated. The curvature of V vs concentration was found to fit the Logan model very well. [ABSTRACT FROM AUTHOR]

[Display omitted] • Weak hydrogen bonding is present in binary solutions. • Simulations of the HB modes with DFT are in good agreement with experiment. • HB and high pressure tune the FR of the CS 2 molecule differently. In the spectroscopic study of polyatomic molecules, Fermi resonance (FR) is a vibrational coupling and energy transfer phenomenon that widely exists intra- and intermolecular. In particular, the FR coupling between the fundamental mode ν 1 and the doubling mode 2ν 2 of the CS 2 molecule has attracted extensive research. In this work, we investigate the effect of local field on tuning the FR of CS 2. By analyzing the Raman spectra of CS 2 mixed with methanol and ethanol with different mole fractions, the results indicated that weak HBs interactions in binary solutions can be reflected by the linear frequency shift of the C–H bond vibrations (in methanol and ethanol) with different molar concentrations. Furthermore, the geometrical structure was optimized using DFT simulation, and the vibration analysis and interaction energy were carried out. The simulated Raman spectra are in good agreement with the experiments. In addition, high-pressure Raman spectra of CS 2 were obtained by diamond anvil cell technique (up to 9.19 GPa) and a pressure-induced phase transition was observed at 1.71 GPa. The results demonstrated that the pressure-induced polymerization phase transition of CS 2 molecules causes the close packing and more orderly arrangement of molecules, resulting in the enhancement of FR coupling. HB and high pressure tune the FR of the CS 2 molecule differently. [ABSTRACT FROM AUTHOR]

[Display omitted] The vibrational dynamics of diborane have been extensively studied both theoretically and experimentally ever since the bridge structure of diborane was established in the 1950s. Numerous infrared and several Raman spectroscopic studies have followed in the ensuing years at ever increasing levels of spectral resolution. In parallel, ab initio computations of the underlying potential energy surface have progressed as well as the methods to calculate the anharmonic vibration dynamics beyond the double harmonic approximation. Nevertheless, even 70 years after the bridge structure of diborane was established, there are still significant discrepancies between experiment and theory for the fundamental vibrational frequencies of diborane. In this work we use parahydrogen (pH 2) matrix isolation infrared spectroscopy to characterize six fundamental vibrations of B 2 H 6 and B 2 D 6 and compare them with results from configuration-selective vibrational configuration interaction theory. The calculated frequencies and intensities are in very good agreement with the pH 2 matrix isolation spectra, even several combination bands are well reproduced. We believe that the reason discrepancies have existed for so long is related to the large amount of anharmonicity that is associated with the bridge BH stretching modes. However, the calculated frequencies and intensities reported here for the vibrational modes of all three boron isotopologues of B 2 H 6 and B 2 D 6 are within ± 2.00 cm−1 and ± 1.44 cm−1, respectively, of the experimental frequencies and therefore a refined vibrational assignment of diborane has been achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • There were two phase transitions of α-HQ found at 3.61 and 12.46 GPa. • Pressure induced 831 cm−1 and 854 cm−1 with the same symmetry at 3.61 GPa. • Pressure provided an effective way to induce fundamental FR phenomenon. Fermi resonance (FR), a prevalent phenomenon in molecules, has an important effect in spectrum analysis. As an effective way to change the molecular structure and tune symmetry, high-pressure techniques can often induce FR. Hydroquinone (HQ) is a hydrogen-bonded crystal that tends to form a solid inclusion compound with a suitable guest and has wide applications. In this work, a high-pressure technique was used to investigate α-HQ using high pressure to tune the symmetry to produce FR. Raman and infrared spectra of α-HQ were investigated at ambient pressure, and then Raman spectra under high pressure of α-HQ were investigated up to 19.64 GPa. Results indicated that there were two phase transitions found at about 3.61 and 12.46 GPa. Fundamental FR was not present in α-HQ molecules at ambient pressure. At 3.61 GPa, the first-order phase transition occurred due to the pressure-induced symmetry change, resulting in two Raman modes at 831 cm−1 and 854 cm−1 with the same symmetry, thereby providing evidence that the fundamental FR phenomenon occurred. Furthermore, the pressure-induced changes of the FR parameters were elucidated. Thus pressure provided an effective way to study FR between two asymmetric species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various concentration of pyridine-ethanol led to different HB strengths. • The two FR of pyridine varied independently with environmental changes. • Pressure tuning the molecular symmetry during the phase transition. The Fermi resonance (FR) phenomenon is prevalent in infrared and Raman spectroscopy, and it can be observed in a variety of molecules. In particular, pyridine is a compound that has two Fermi doublets: ν 1 ∼ ν 12 and ν 1 + ν 6 ∼ ν 8. To analyze the effect of environmental changes on the FR, this study first investigated the Raman spectra of pyridine mixed with ethanol at different concentrations. Results indicated that the FR parameters exhibited a nonlinear dependence on the pyridine concentration fractions, and changing the concentration fraction of pyridine led to different hydrogen bond strengths. Second, the interaction mechanism of pyridine-ethanol binary solutions was analyzed by two-dimensional correlation Raman spectroscopy (2DCRS). In addition, high-pressure Raman spectra of a 50% pyridine-ethanol binary solution were measured up to a pressure of 19.65 GPa by a diamond anvil cell technique, and the phase transition of the binary solution occurred at 6.35 GPa. Finally, the impact of ethanol on the FR of pyridine was determined by deducing the FR parameters at different pressures. The turning point at 6.35 GPa was consistent with the Raman frequency–pressure relationships. The results demonstrated that changes in the intensity of ν 1 did not affect the FR of ν 1 + ν 6 ∼ ν 8 , whereas the undisturbed frequency ν 1 still played a role in the FR. When the pressure was compressed to 13.36 GPa, the disappearance of the Raman peaks (ν 1 and ν 1 ′) was attributed to the tuning of the molecular symmetry by pressure during the phase transition. [ABSTRACT FROM AUTHOR]

High-resolution infrared (IR) reduced-Doppler absorption spectra of jet-cooled gas phase trans -formic acid in the v 1 OH stretching fundamental region are reported for the first time, obtained by supersonically expanding trans- formic acid/Ar mixtures through a slit jet nozzle source and rotationally cooling to T rot ≈ 10.9(5) K, with absorption signals recorded by high-resolution difference-frequency IR absorption spectroscopy. Two a / b -type rovibrational bands of comparable intensity, one ∼10-fold weaker b -type band, and one ∼6-fold weaker a -type band are observed, with vibrational band origins at 3570.493(5), 3566.793(5), 3560.032(9), and 3534.6869(2) cm−1, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibert [A. Nejad, E.L. Sibert III, The Raman jet spectrum of trans -formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database, J. Chem. Phys. 154(6) (2021) 064301.], these four rovibrational bands have been assigned to v 1 , (v 2 + v 7), (v 6 + 2 v 7 + 2 v 9), and 2 v 3 , respectively. Specifically, two of the three upper dark states (2171 (a ′) and 617292 (a ′)) are close enough to the "bright" 11 (a ′) state to facilitate strong anharmonic resonance interactions, which results in intensity mixing into the two zero-order bands that would otherwise be "dark". Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between these zero-order 11 and 2171 states resulting in extra lines (i.e., some upper levels in the nominally v 1 band have majority zero-order 2171 state character). This motivates development of a 3 coupled state (11, 2171, and 617292) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate (> 2) coupling. Though limited by range of J and K a levels (J' ≤ 9 and K a ' ≤ 3) populated at supersonic jet temperatures, this work offers first precision spectroscopic analysis of trans -formic acid in the v 1 OH stretch region, which should aid in assignment of the more complete yet highly congested room temperature FTIR spectra [D. Hurtmans, F. Herregodts, M. Herman, J. Liévin, A. Campargue, A. Garnache, A. Kachanov, Spectroscopic and ab initio investigation of the ν OH overtone excitation in trans -formic acid, J. Chem. Phys. 113(4) (2000) 1535–1545.]. Finally, and in sharp contrast to the spectral complexity in the three predominantly b -type bands, the lone a -type 2 v 3 rovibrational band at 3534.6869(2) cm−1 is well described by a simple, rigid asymmetric top Hamiltonian. [Display omitted] • Jet-cooled trans -formic acid at T rot ≈ 11 K is obtained by supersonic expansion through a slit jet nozzle source. • The v 1 band region of jet-cooled trans -HCOOH has been recorded using a high-resolution difference-frequency IR spectrometer. • Four rovibrational bands are observed between 3528 and 3583 cm-1 and rovibrationally analyzed for the 1st time. • Strong Fermi/anharmonic resonance interactions between the bright 11 and nearby dark 2171, 617292 states are found. • Rotation of v 1 transition dipole moment direction is observed, possibly due to charge-sloshing or proton transfer effects. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four frequencies have been observed in the iso and aniso Raman spectra of EC. • Fermi constant W, NCE value V1 and V2 have been determined at different concentration. • Dimer structure and DFT calculations can reproduce the NCE and concentration effects. The vibration band of the ring stretching (ν 14), the fundamental ring breathing (ν 17) and the Fermi resonance band of carbonyl stretching mixing with the overtone of the ring breathing (ν 5 + 2ν 17) have been investigated in solid ethylene carbonate (EC) and EC/CH 3 CN and EC/CHCl 3 binary mixture. Dimer structure with aggregation-induced spectral splitting model (AIS) was applied to calculate the vibration spectra using the B3LYP-D3/6-311+G (d,p) procedure. The noncoincidence effect (NCE) and concentration induced frequency shifts of the ν 14 and ν 5 could be well explained by AIS model based on the dimer structure. Four bands were observed with two in the isotropic and two in the anisotropic Raman spectra and their NCE value decreased with the decrease of EC volume fraction in the binary mixture, and finally disappeared. NCE value and the Fermi resonance constants of EC at different concentrations were calculated from the experimental data. [ABSTRACT FROM AUTHOR]

Direct optimal control theory for quantum dynamical problems presents itself as an interesting alternative to the traditional indirect optimal control. The method relies on the first discretize and then optimize paradigm, where a discretization of the dynamical equations leads to a nonlinear optimization problem. It has been applied successfully to the control of a bistable system where the wavepacket was approximated by a parameterized Gaussian, leading to a semiclassical set of equations of motion (A. R. Ramos Ramos, O. Kühn, Front. Phys. 9 (2021) 615168). Motivated by these results, in the present paper we extend the application of the method to the case of exact wavepacket propagation using the example of a generic Fermi-resonance model. In particular we address the question how population of the involved overtone state can be avoided such as to reduce the effect of intramolecular vibrational energy redistribution. A methodological advantage is that direct optimal control theory offers flexibility when choosing the running cost, since there is no need to compute functional derivatives and coupling terms as in the case of indirect optimal control. We exploit this fact to include state populations in the running cost, which allows their optimization. [ABSTRACT FROM AUTHOR]

In situ high-pressure Raman spectra of phthalic anhydride (PA) have been measured up to 16 GPa through diamond anvil cell technique. The results show that all the Raman bands are blue-shifted with the increase of pressure, accompanied by appearance of some new bands. A Fermi resonance phenomenon of the two Raman fundamental modes of PA at 773 cm -1 and 801 cm -1 is proposed at pressures above 6.6 GPa, where a possible first-order phase transition occurs. The pressure-induced changes of Fermi resonance parameters, e.g., intensity ratio, coupling coefficient and frequency gap of unperturbed transition, are discussed., (© 2022 IOP Publishing Ltd.)