Abstract

A Nd:YAG pumped frequency-doubled dye laser is used to excite X²π, v″ = 1, N′ OH radicals to a specific N' state of A²Σ⁺, v′ = 1. OH radicals are produced in a differentially pumped flow system by the reaction of H atoms produced by a microwave discharge in a molecular hydrogen and NO₂. The total energy transfer rate, k_T, is determined by monitoring the time decay of single rotational fluorescence lines as a function of colliding gas pressure. Using nitrogen as a colliding gas, k_T is found to decrease from (6.4 ± 0.3) × 10⁻¹⁰ cm³ for excitation in N' = 0 to (4.0 ± 0.2) × 10⁻¹⁰ cm³/s for excitation in N' = 4. In the absence of colliding gas, the fluorescence lifetime of OH is observed to lengthen in regular fashion with increasing N' from 594 ns for N' = 0 excitation to 667 ns for N' = 4 excitation. The k_T is made up of the electronic quenching rate, the rotational energy transfer rate, and the vibrational energy crossover rate. The vibrational crossover rate is determined for specific N' excitations by integrating the rotationally resolved 0 → 0 and 1 → 1 vibrational bands in OH fluorescence spectra between 3060 and 3180 Å as a function of N' and colliding gas pressure. The electronic quenching rate is determined by monitoring the time decay of OH fluorescence in the 1 → 1 vibrational band as a function of colliding gas pressure.

© 1986 Optical Society of America