15min:
MEASUREMENT OF CH3D ABSORPTION CROSS SECTIONS, PRESSURE BROADENING, AND SHFT COEFFICIENTS IN THE 1.65 µm SPECTRAL REGION BY USING CONTINUOUS AVE CAVITY RING-DOWN SPECTROSCOPY.

YONGXIN TANG, SHAOYUE L. YANG, KEVIN K. LEHMANN, Department of Chemistry and School of Medicine, University of Virginia, Charlottesville VA, 22904-4319; D. CHRIS BENNER, Department of Physics, College of William and Mary, Box 8795, Williamsburg, VA 23187-8795.

Quantitative spectroscopy of CH3D in the near-IR is of importance for an ongoing project to build an instrument to measure the H/D isotopic ratio of methane gas. Continuous-wave cavity ring-down spectroscopy (CRDS) has been used to examine the absorption cross sections, the pressure-broadening and pressure-shift coefficients at around 1652 nm. The absorption cross sections of CH3D were quantified in the wavenumber region between 6046 and 6060 cm-1. The maximum peak is located at 6055.17 cm-1, which gives (8.58 \pm 0.37) × 10-21 cm2/molecule at the total pressure of sim 8.2 Torr of the N2 buffer gas. By using the small step size of the laser wavenumber scan, we measured the pressure-broadening effects, and the pressure-shift effects, on CH4 and CH3D absorption lines. The N2, O2 and CO2 pressure broadening coefficients of CH3D are 0.058, 0.054 and 0.049 cm-1/atm, respectively, at the wavenumber we employed. Under the experimental conditions we used, N2 and O2 have very similar pressure broadening effects, and their effects on CH3D is very similar to those of CH4. At the wavenumber we employed, the same values of N2 and O2 pressure-shift coefficient , - 0.012 cm-1/atm, and a little higher value of CO2, - 0.013 cm-1/atm, were found.