Determination of self- and H 2-broadening and shift coefficients in the 2-0 band of [formula omitted] using a multispectrum fitting procedure

Abstract

Self- and hydrogen-broadening coefficients and pressure-shift coefficients for the first overtone band transitions of 12 C 16 O at room temperature have been determined through analysis of nine high-resolution (0.0055 cm −1) absorption spectra. These spectra were recorded using the 1-m Fourier transform spectrometer (FTS) at the McMath-Pierce facility of the National Solar Observatory on Kitt Peak, Arizona. Because of the short path length of the sample cell (10.0 cm) , the volume mixing ratios of CO in hydrogen were relatively high, ∼18–22%, to achieve measurable absorption. These large volume-mixing ratios necessitated the simultaneous determination of the CO self-broadening and self-shift coefficients along with the hydrogen-broadening and hydrogen-induced shift coefficients. We have determined these coefficients at room temperature, along with line positions and absolute intensities, for the P(27) through R(27) 12 C 16 O 2-0 transitions by fitting the entire spectral interval from 4130 to 4345 cm −1 in all nine spectra simultaneously using our multispectrum nonlinear least-squares procedure. Our intensity measurements are consistently low (1–6%) compared with the HITRAN values but the majority of the intensities are within 4% of the HITRAN values. The values of self-broadening coefficients vary from 0.0452 to 0.0862 cm −1 atm −1 at 296 K and those of hydrogen-broadening coefficient range between 0.0475 and 0.0795 cm −1 atm −1 at 296 K . All of our measured self- and hydrogen-shift coefficients are negative and range from −0.002 to −0.008 cm −1 atm −1 . With the pressure and path length used in our study we did not find evidence of significant line mixing in either the self- or hydrogen-broadened spectra. This study represents the first high-resolution experimental determination of hydrogen-induced pressure broadening and pressure-shift coefficients in the 2-0 band of 12 C 16 O at room temperature.