Diode Laser Measurements of Self-Broadening Coefficients in the v5-Band of C2H2 at Low Temperature

Collisional self-broadening coefficients for 21 lines in the P and R branches of the v5 band of C2H2 at low temperature (173 K) have been measured using a tunable diode laser spectrometer and a low-temperature variable path length absorption cell. These lines, with J values ranging from 1 to 25, are located in the spectral range 670-790 cm−1. A semiclassical line-broadening calculation provides satisfactory results when the electrostatic interactions arising from the hexadecapole moment of C2H2 are taken into account. We have also examined the validity of a simple power law governing the temperature dependence of the broadening coefficients.