Journal of Physical Chemistry A, Vol.111, No.50, 13182-13192, 2007
Resonance Raman intensity analysis of the excited-state proton-transfer dynamics of 2-hydroxybenzaidehyde in the charge-transfer/proton-transfer absorption band
Resonance Raman spectra were obtained for 2-hydroxybenzaldehyde (OHBA) in cyclohexane solution with excitation wavelengths in resonance with the first charge-transfer/proton-transfer (CT/PT) band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal C=CH in-plane bend + ring deformation modes (v(9), v(10), v(14), v(16), v(18), v(19), v(20), v(26), v(30), v(31), and v(35)) accompanied by a smaller amount of motion along the nominal C=O stretch mode (v(7)) the nominal C=C-C(=O) in-plane bend modes (v(33) and v(37)), and the nominal ring C-O-H in-plane bend modes (v(9) and v(14)). A preliminary resonance Raman intensity analysis was done, and these results for the OHBA molecule were compared to results previously reported for the 2-hydroxyacetophenone (OHAP) molecule. Several proton-transfer tautomers in the ground and excited states were predicted from the results of B3LYP/cc-PVTZ, UB3LYP/cc-PVTZ, and CASSCF/cc-PVDZ level of theory computations. The differences and similarities between the CT/PT band resonance Raman spectra and the vibrational reorganizational energies for the OHBA molecule relative to those for the OHAP molecule are briefly discussed.