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Resonance Raman spectra were obtained for benzamide in methanol and acetonitrile solutions with excitation wavelengths in resonance with the S3 state. These spectra indicate that the Franck–Condon region photodissociation dynamics have multidimensional character with the motions mainly along the benzene ring C==C stretch ν9, the Ph–CO–NH2 and ring benzene stretch ν14, the CCH in plane bend ν17, the Ph–CO–NH2 stretch and NH2 rock ν19, the ring trigonal bend ν23, and the ring deformation and Ph–CO–NH2 stretch ν29. A preliminary resonance Raman intensity analysis was done, and the results were compared to those previously reported for acetophenone to examine the substituent effect. Solvent effect on the short-time photodissociation dynamics of benzamide was also examined. A conical intersection point S2/S3 between S3 and S2 potential energy surfaces of benzamide was determined by using a complete active space self-consistent field theory computations. The structural differences and similarities between S3/S2 point and S0 were examined, and the results were used to correlate to the Franck–Condon photodissociation dynamics of benzamide in S3 state. [ABSTRACT FROM AUTHOR]

The structural dynamics of 4-pyrimidone (4PMO) in the A- and B-band absorptions was studied by using the resonance Raman spectroscopy combined with quantum chemical calculations to better understand whether the excited state intramolecular proton-transfer (ESIPT) reaction occurs in Franck-Condon regions or not. The transition barrier for the ground state proton-transfer tautomerization reaction between 3(H) (I) and hydroxy (II) was determined to be 165 kJ·mol−1 in vacuum on the basis of the B3LYP/6-311++G(d,2p) level of theory calculations. Two ultraviolet absorption bands of 4PMO were, respectively, assigned as πH→π*L and πH→π*L+1 transitions. The vibrational assignments were done on the basis of the Fourier transform (FT)-Raman and FT-infrared (IR) measurements, the density-functional theory computations and the normal mode analysis. The A- and B-band resonance Raman spectra of 4PMO were measured in water, methanol and acetonitrile. The structural dynamics of 4PMO was obtained through the analysis of the resonance Raman intensity pattern. We discuss the similarities in the structural dynamics of 4PMO and 2-thiopyrimidone (2TPM), and the results were used to correlate to the intramolecular hydrogen-atom-transfer process as observed by matrix-isolation IR experiments for 4PMO. A variety of NH/CH bend modes + C = O stretch mode mark the hydrogen-detachment-attachment or ESIPT reaction initiated in Franck-Condon region for 4PMO and 2TPM. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The A-band resonance Raman spectra were obtained for methyl xanthate anion in methanol solution. Density functional calculations were done to help elucidate its ultraviolet electronic transitions and to assign the resonance Raman spectra. The results indicate that the Franck–Condon region photodissociation dynamics have multidimensional character with motion predominantly along the symmetric CS2 stretch, accompanied by the COC stretch, the CH3 wag, the COC scissor, the CS2 scissor, and overtone of the OCS2 out of plane deformation. RCIS/6-31G∗ calculations were done to predict the distorted geometry structure and the saddle point of methyl xanthate anion in S3 excited state. [Copyright &y& Elsevier]

Resonance Raman spectra were obtained for 2-nitrophenol in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) proton transfer band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion along more than 15 normal modes: the nominal CCH bend+CC stretch ν12 (1326 cm-1), the nominal CCC bend ν23 (564 cm-1), the nominal CO stretch+NO stretch+CC stretch ν14 (1250 cm-1), the nominal CCH bend+CC stretch+COH bend ν15 (1190 cm-1); the nominal CCH bend+CC stretch ν17 (1134 cm-1), the nominal CCC bend+CC stretch ν22 (669 cm-1), the nominal CCN bend ν27 (290 cm-1), the nominal NO2 bend+CC stretch ν21 (820 cm-1), the nominal CCO bend+CNO bend ν25 (428 cm-1), the nominal CC stretch ν7 (1590 cm-1), the nominal NO stretch ν8 (1538 cm-1), the nominal CCC bend+NO2 bend ν20 (870 cm-1), the nominal CC stretch ν6 (1617 cm-1), the nominal COH bend+CC stretch ν11 (1382 cm-1), nominal CCH bend+CC stretch ν9 (1472 cm-1). A preliminary resonance Raman intensity analysis was done and the results for 2-nitrophenol were compared to previously reported results for nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. The authors briefly discuss the differences and similarities in the CT-band absorption excitation of 2-nitrophenol relative to those of nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. [ABSTRACT FROM AUTHOR]

The resonance Raman spectroscopic study of the excited state structural dynamics of 1,3-dimethyluracil (DMU), 5-bromo-1,3-dimethyluracil (5BrDMU), uracil, and thymine in water and acetonitrile were reported. Density functional theory calculations were carried out to help elucidate the ultraviolet electronic transitions associated with the A-, and B-band absorptions and the vibrational assignments of the resonance Raman spectra. The effect of the methylation at N1, N3 and C5 sites of pyrimidine ring on the structural dynamics of uracils in different solvents were explored on the basis of the resonance Raman intensity patterns. The relative resonance Raman intensities of DMU and 5BrDMU are computed at the B3LYP-TD level. Huge discrepancies between the experimental resonance Raman intensities and the B3LYP-TD predicted ones were observed. The underlying mechanism was briefly discussed. The decay channel through the S1(1nπ*)/S2(1ππ*) conical intersection and the S1(1nπ*)/T1(3ππ*) intersystem crossing were revealed by using the CASSCF(8,7)/6-31G(d) level of theory calculations. [ABSTRACT FROM AUTHOR]

The structural dynamics of thioanisole in the S2(ππ*) electronic state that has large oscillator strength was studied by using the resonance Raman spectroscopy. The vibrational assignments were done for thioanisole on the basis of the FT-Raman and FT-IR measurements, the density-functional theory computations and the normal mode analysis. The A- and B-band resonance Raman spectra were obtained in cyclohexane, methanol and acetonitrile, in which ten modes in A' irreducible representations were observed. The structural dynamics were obtained according to the resonance Raman intensity pattern. The vibroinc-coupling between the S3(πσ*) electronic state that has no oscillator strength and the S2(ππ*) electronic state were revealed. We discuss the correlation between our present structural dynamics and the previous S2(ππ*)/S3(πσ*) conical intersectional dynamics revealed by resonant-enhanced two-photon ionization and the photofragment excitation spectroscopic study. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The photophysics and photochemistry of pyrazine (C4H4N2, D2h) after excitation to the S2 (1 1B2u, 1ππ*) electronic state were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The B-band resonance Raman spectra in cyclohexane solvent were obtained at 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of pyrazine in the S2 (1 1B2u, 1ππ*) state. Three electronic states 1 1B3u, 1 1B1g, and 1 1B2g were found to couple with the S2 (1 1B2u, 1ππ*) state. Two conical intersection (CI) points CI[ S2(B2u)/ S1(B3u)] and CI[ S1/ S0] and one transition state of the isomerization between pyrazine and pyrimidine were predicted to play important roles in the photochemistry of pyrazine. On the basis of the calculations, the mechanism of the photoisomerization reaction between pyrazine and pyrimidine has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: FT-Raman and/or FT-IR spectra of 3-amino-2-cyclohexen-1-one (ACyO) in solid state and/or in solvents of water and acetonitrile were obtained. Density functional theory calculations were done to help elucidate the vibrational band assignments. The A-band resonance Raman spectra of ACyO were acquired in water and acetonitrile solvents to examine the excited state structural dynamics and the state-mixing or curve-crossing tuned by solvents. A preliminary resonance Raman intensity analysis using the time-dependent wave-packet theory and simple model was done for ACyO in acetonitrile solvent. Resonance Raman spectroscopic probing of the excited state curve-crossing or state-mixing was proposed. [Copyright &y& Elsevier]

The resonance Raman spectra were obtained for both 2-thiopyridone (2TP) and its proton-transfer tautomer 2-mercaptopyridine (2MP) in water solution. Density functional theory (DFT) calculations were carried out to help elucidate their ultraviolet electronic transitions and vibrational assignments of the resonance Raman spectra associated with their B-band absorptions. The nanosecond time-resolved resonance Raman spectroscopic experiment was carried out to further confirm the assignment that the transient species was the ground state 2MP. The different short-time structural dynamics were examined for both 2TP and 2MP in terms of their resonance Raman intensity patterns. The transition barriers between 2TP and 2MP for S0, T1, and S1states are determined by using (U)B3LYP-TD and CASSCF level of theory computations, respectively. The excited state proton transfer (ESPT) reaction mechanism is proposed and briefly discussed. [ABSTRACT FROM AUTHOR]