Diode-laser measurements of He-, Ar-, and N-2-broadened HF lineshapes in the first overtone band

High-resolution lineshapes of the HF P(3) and P(6) transitions (2-0 band) h ave been recorded in a 14.9-cm long absorption cell (T = 296 K) using a pai r of (InGaAsP)-distributed feedback diode lasers operating near 1.31 and 1. 34 mu m, 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 N-2. Motional narrowing was observed for the He-broadened lineshapes over a ran ge of total pressures from 50 to 646 Torr. The Ar- and N-2-brondened spectr a showed a strong narrowing effect for pressures less than 400 Torr. At hig her pressures, narrowing parameters could not be reliably determined due to the relatively large Ar- and N-2-pressure broadening. The collision widths inferred from Voigt-profile fits were systematically less than those deter mined from Rautian and Galatry fits (up to 25% for the He-broadened P(6) tr ansition). 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 measu red shifts were 10 and 20% less than calculated values for the P(3) and P(6 ) transitions, respectively. The measured N-2-broadening and shift coeffici ents agree reasonably well with values determined from previous experiments . (C) 1999 Academic Press.