Collision broadening of OH emission lines, measured in the infrared

Abstract

The OH emission spectrum from an H2/O2 flame was recorded in the infrared, for the (1, 0) vibrational transition of the ground 2IIi state. The spectral region covered was 3.18 to 3.65 μ [four lines each for P(10) to P(18)]. Use of a high-resolution spectrometer with a slit width (full width at half maximum) of 0.06 to 0.04 cm−1 allowed the direct estimation of linewidths, which were found to range from 0.11 cm−1 for the P(10) lines to 0.08 cm−1 for the P(18) lines. The deduced collision linewidths for the fundamental vibrational band in the ground state are larger than expected on the basis of comparable data for HCl, and are about five times greater than those reported for the (0, 0) band of the 2Σ+→2IIi transition, measured in the ultraviolet. A theoretical estimate of the dipole-induced dipole, dispersion forces and hardcore contributions to the OH linewidth, under flame conditions, gave a value of ≈0.03 cm−1. It is suggested that resonance and near-resonance effects between energy-level spacings for OH and H2O (in the infrared) are the cause of the large linewidths.