Comparison of motionally narrowed coherent anti-Stokes Raman spectroscopy line shapes of H_2 with hard- and soft-collision models

We have compared high-resolution coherent anti-Stokes Raman spectroscopy measurements of the Q(1) transition of H(2) with theoretical line shapes incorporating both Doppler broadening and motional narrowing. Least-squares fits varying the motional narrowing coefficient for both the hard- and soft-collision model yielded line shapes that agreed well with observed spectra at 295 K for pressures between 50 and 3050 Torr. However, the narrowing coefficient for the hard-collision model was pressure dependent, whereas the narrowing coefficient for the soft-collision model was independent of pressure and yielded an optical diffusion coefficient that agreed with previously measured values.