Rate-equation modeling of single- and multiple-quantum vibrational energy transfer of OH (A 2Σ+, v′=0 to 3)

Abstract.

A computer code based on a kinetic rate-equation model for describing the collisional dynamics of OH (A ²Σ⁺) in laser-induced fluorescence experiments was developed. In this work, the capabilities of the simulation code are extended to include the vibrational states up to the OH (A ²Σ⁺, v^′=3) level. The calculation of quenching, rotational and vibrational relaxation rate coefficients for different collider species is discussed. Problems that arise for the description of vibrational relaxation include the branching ratio between single- and multiple-quantum steps and the form of the nascent rotational distribution after a vibrational relaxation step. Experimental spectra recorded under a variety of conditions are simulated using a consistent set of model assumptions. The calculations must include vibrational relaxation steps up to Δv=3 to account for the experimental intensity distributions. Effects due to polarized laser excitation become more important for vibrational states with v^′>1. Areas for future work are identified, including determination of experimental rate coefficients for state-changing and depolarizing collisions in the upper vibrational levels.