Self- and N2- broadening of CO in the low-pressure regime

Sub-Doppler saturated absorption spectroscopy of rovibrational transitions of carbon monoxide broadened by nitrogen was recorded at low pressures (1-24 Pa) near 1.56 µm with comb-locked cavity ring-down saturation spectroscopy. We found a nonlinear pressure dependence of the Lamb-dip width of the CO transition induced by elastic scattering. Analysis of the results allows us to characterize parameters of elastic- and nonelastic- scattering under collisions. The elastic scattering angle for nitrogen-induced collisions (CO-N2) was determined to be larger than 0.6 × 10−3 rad. The line broadening of the Lamb dip in the region of low pressures exceeds the broadening at high pressures by a factor of 4 and 5 for the self- and N2-broadening CO R(9) transition. Moreover, much smaller line shifts for both self- and N2-broaden Lamb dips were observed, which was also attributed to the decrease in the number of scattered molecules in the interaction and the increasing attracting forces.