COLLISION BROADENING AND SHIFT OF NO GAMMA(0,0) ABSORPTION-LINES BY O2 AND H2O AT HIGH-TEMPERATURES

Collision-broadened absorption lineshapes of the A <-- X(0,0) transitions of NO near 225 nm were measured behind reflected shock waves in a shock tube by using the frequency-doubled output of a narrow-linewidth, rapid-tuning cw ring dye laser. The profiles of the transitions, perturbed by a single bath species, either H2O or O2, were fit assuming Voigt lineshapes to derive collision-induced width coefficients (2gamma). The collision-induced shift coefficient (delta) was also measured, with reference to the same NO feature recorded simultaneously in absorption across a low-pressure cell of pure NO. For both perturbers, an inverse power-law for the temperature dependence was obtained for both 2gamma and delta. Over the temperature range 1000-2000 K, 2gamma for the case of O2 as perturber was roughly 80% of that measured for the case of H2O as perturber, and delta for both perturbers were the same within approximately 10%. Dependences of 2gamma and delta on the ground-state energy of the A <-- X (0,0) transitions of NO were discernible for the case of H2O as perturber. All perturbers induced slight asymmetries and narrowing of the lineshape.