Determination of line intensity and pressure broadening of the 619.68 nm methane overtone absorption line at low temperatures using intracavity laser spectroscopy

Intensity Measurements and Collision-Broadening Coefficients for the Oxygen A Band Measured by Intracavity Laser Absorption Spectroscopy

“…The results are given in Table 1e. For the most part, there are no significant differences among the broadening coefficients (for a given N) for 16 16 O 2 , he found that the broadening coefficients were some 25% smaller than for selfbroadening of the 16 O 2 lines. This is not easily explained in view of the fact that the mixed isotope has all rotational levels occupied (as can readily be seen in Fig.…”

“…A simple "energy-gap" scaling argument might suggest that the higher "density of states" and correspondingly smaller energy spacings between adjacent rotational levels in the mixed isotope of oxygen would facilitate rotationally inelastic collisions, which are primarily responsible for collision broadening. While this could be partially mitigated by the lack of "resonance" between 16 O 18 O and 16 O 2 , such "resonance defects" are small and should not make a large difference for inelastic collision probabilities.…”

“…Nitrogen-broadening coefficients of the 16 O 2 N ϭ 9 and N ϭ 11 doublets and self-broadening coefficients of high N and hot-band transitions were determined using both the LC and RC configurations. Measurements on the N ϭ 9 and N ϭ 11 doublets were carried out with a generation time of 80 s, keeping the oxygen pressure constant at 0.8 Torr and varying the nitrogen pressure from 50 to 770 Torr.…”

“…Pressure-broadened linewidths for the N ϭ 9 and N ϭ 11 A-band doublets were measured using both the LC and RC configurations. The pressure-broadening coefficients for the 16 O 2 lines are given in Table 1d and compared with Brown's measurements for the same set of lines (7). The mutual agreement between our two data sets and the LB measurements is excellent, thereby further validating the ICLAS technique and our fitting procedure for linewidth determination.…”

“…With this technique, effective pathlengths of tens to hundreds of kilometers through the sample can be achieved, overcoming many of the sensitivity limitations noted above. By careful control of the ICLAS generation time t g 1 and data acquisition procedure (12), it is possible to carry out quantitative lineshape measurements, as has been demonstrated for water vapor (14,15), methane (16), and the (vЈ ϭ 2) 4 (vЉ ϭ 0) band of the O 2 b 4 X transition (␥ band) (17,18).…”