Rotational Contour Analysis of Jet-Cooled Methyl Hydroperoxide Action Spectra in the Region of the 2νOH and 3νOH Bands

Abstract

State-selected photodissociation is used to record the partially rotationally resolved action spectra of CH(3)OOH in the region of its first and second OH-stretching overtones (2nu(OH) and 3nu(OH)) under free-jet expansion conditions. From an analysis of the rotational band contours for the OH-stretching states and their corresponding COOH torsion combination bands, effective rotational constants and transition dipole moment orientations are determined for the vibrational eigenstates. The level splitting between the lowest symmetric and antisymmetric pair of COOH torsion levels, 0(+) and 0(-), associated with the 2nu(OH) overtone state is found to be approximately 3.9 cm(-1). Comparison of spectra in the region of the 2nu(OH) and 2nu(OH) + nu(COOH) bands in CH(3)OOH and CD(3)OOH reveals that the spectral features in CH(3)OOH are substantially more perturbed compared to those of its deuterated counterpart, suggesting that modes involving the methyl rotor contribute significantly to promoting intramolecular vibrational energy redistribution (IVR) in CH(3)OOH. Furthermore, a comparison of the average rotational line widths in both CH(3)OOH and CD(3)OOH for the 2nu(OH) and 2nu(OH) + nu(COOH) bands appears to suggest that at these energies, adding one quanta of low-frequency COOH torsional motion does not enhance the IVR rate relative to that of the pure OH-stretching overtone.