Rate-equation modeling of single- and multiple-quantum vibrational energy transfer of OH (A (2)Sigma(+), upsilon ' = 0 to 3)

A computer code based on a kinetic rate-equation model for describing the c ollisional dynamics of OH (A (2)Sigma(+)) in laser-induced fluorescence exp eriments was developed. In this work, the capabilities of the simulation co de are extended to include the vibrational states up to the OH (A (2)Sigma( +), upsilon' = 3) level. The calculation of quenching, rotational and vibra tional relaxation rate coefficients for different collider species is discu ssed. Problems that arise for the description of vibrational relaxation inc lude 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 simu lated using a consistent set of model assumptions. The calculations must in clude vibrational relaxation steps up to at, = 3 to account for the experim ental intensity distributions. Effects due to polarized laser excitation be come more important for Vibrational states with upsilon' > 1. Areas for fut ure work are identified, including determination of experimental rate coeff icients for state-changing and depolarizing collisions in the upper vibrati onal levels.