Calculations of the low temperature pressure broadening of HCO+ rotational spectral lines by H2

Calculations on the pressure broadening by H2 of HCO+ rotational spectral lines have been performed in the temperature range 11–300 K. Recent low temperature measurements of the pressure broadening of the J=3–2 line at 11–30 K are reproduced to within 10–20% by the results of a capture theory. The results of Anderson theory in this temperature range, on the other hand, are low by a factor of up to ≊3 compared with experiment. A hybrid method is proposed, which converges to the capture theory at low temperatures and the Anderson theory at high temperatures.