OH stretch overtone spectroscopy and transition dipole slignment of HOD
David Nesbitt, J R. Fair, O Votava
Photoscoustic spectroscopy in room-temperature H2O/HOD/D2O cells has been used to probe the 3vOH and 4vOH overtone bands in HOD via excitation with a single mode (160 MHz) injection-seeded optical parametric oscillator (OPO) and pulsed dye laser, respectively. Transitions corresponding to HOD are isolated by compresion between H2O/HOD/D2O and pure H2O overtone spectra and are analyzed with a Watson asymmetric top Hamiltonian. Least-squares fits yield the vibrational dependence of AvBvand Cv rotational constants as well as Birge-Sponer analysis of the vibrational overtone series for up to vOH=4. Relative intensities of a-type and b-type bands are reported for 3vOHand 4vOH which indicate that the transition dipole moment vector tilts away from the OH bond with increasing vdOH^ excitation. This observation is qualitatively inconsistent with simple local-mode, bond-dipole model predictions of the vibrational dynamics. However, the results are in excellent agreement with full 3D quantum variational calculations based on the H2O potential of Polyansky, et al. [J. Chem. Phys. 105, 6490 (1996)] and dipole moment surface of Gabriel, et al. [J. Chem. Phys. 99,897(1993)].