Anomalies of pressure broadening in the H-2 S-0(3) transition versus perturber concentration

Inhomogeneous broadening in vibrational Q lines for H-2 broadened by heavy rare gases due to speed-changing collisions was previously demonstrated through the nonlinear behavior of the linewidths versus the concentration. In order to explore a possible inhomogeneous broadening (similar mechanism) for a pure rotational relaxation mechanism, the broadening and line shift of the pure rotational quadrupole transition S-0(3) of H-2 have been measured to high precision with a frequency stabilized diode laser spectrometer. Foreign gas effects with helium and argon at various dilution ratios in H-2 have been investigated. A nonlinear dependence of the broadening on the mixing ratio was detected in a pure rotational transition for the H-2-Ar mixture. This is the spectral signature expected for an inhomogeneous broadening due to speed-changing collisions.