Diode–Laser Measurements of He-, Ar-, and N2-Broadened HF Lineshapes in the First Overtone Band

Abstract

High-resolution lineshapes of the HF P(3) and P(6) transitions (2–0 band) have been recorded in a 14.9-cm long absorption cell (T = 296 K) using a pair of (InGaAsP)-distributed feedback diode lasers operating near 1.31 and 1.34 μm, respectively. The absorption lineshapes were least-squares fit to Voigt, Rautian, and Galatry profiles to determine the collision widths and velocity-changing collision frequencies for the perturbers He, Ar, and N2. Motional narrowing was observed for the He-broadened lineshapes over a range of total pressures from 50 to 646 Torr. The Ar- and N2-broadened spectra showed a strong narrowing effect for pressures less than 400 Torr. At higher pressures, narrowing parameters could not be reliably determined due to the relatively large Ar- and N2-pressure broadening. The collision widths inferred from Voigt-profile fits were systematically less than those determined from Rautian and Galatry fits (up to 25% for the He-broadened P(6) transition). The measured pressure-induced broadening and shift coefficients were compared with other experimental data and full-quantal close-coupling (CC) scattering cross-section calculations. The measured Ar-broadening half-widths were in excellent agreement with calculated values, while the measured shifts were 10 and 20% less than calculated values for the P(3) and P(6) transitions, respectively. The measured N2-broadening and shift coefficients agree reasonably well with values determined from previous experiments.