H 2-broadening coefficients in the ν2 and ν4 bands of PH 3

Abstract

H 2-broadening coefficients are measured for 41 transitions of PH 3 in the QR branch of the ν 2 band and the PP , RP , and PQ branches of the ν 4 band, using a tunable diode-laser spectrometer. The recorded lines with J values ranging from 2 to 16 and K from 0 to 11 are located between 995 and 1106 cm −1 . The collisional widths are determined by fitting each spectral line with a Voigt profile, a Rautian profile, and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. These coefficients γ 0( J, K) are found to decrease slightly on the whole as J increases and they decrease significantly for K values approaching or equal to J (J⩾4) . The H 2-broadenings are also calculated on the basis of a semiclassical model of interacting linear molecules, using an atom–atom Lennard-Jones potential in addition to the weak electrostatic contributions. The theoretical results are in satisfactory agreement with the experimental data and reproduce the J and K dependencies of the broadenings, but the decrease observed for the QR(J,K) transitions with K= J is notably overestimated.