Pressure broadening of the HCO+ J=0–1 transition by hydrogen

Measurements have been made of the broadening of the HCO+ J=0–1 microwave absorption line by hydrogen. The linewidths (Δν, half-width at half-intensity) were obtained from a nonlinear least squares analysis of the individual spectra, taken over the pressure range of 4–40 mTorr. The pressure dependence of the linewidth, dΔν/dP was determined to be 29.6±3 MHz/Torr for the HCO+ transition broadened by H2 near 100 °K. This corresponds to a collisional cross section of 182±20 Å2 for HCO+–H2. Also, a new and more reliable measurement is reported for broadening of the J=7–8 transition of 18OCS, which gives dΔν/dP=7.11±0.15 MHz/Torr for self-broadening at 296 °K.