Determination of self- and H2-broadening and shift coefficients in the 2-0 band of 12C16O using a multispectrum fitting procedure

Self- and hydrogen-broadening coefficients and pressure-shift coefficients for the first overtone band transitions of 12C16O at room temperature have been determined through analysis of nine high-resolution (0.0055cm−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 (10.0cm), 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) 12C16O 2-0 transitions by fitting the entire spectral interval from 4130 to 4345cm−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 0.0862cm−1atm−1 at 296K and those of hydrogen-broadening coefficient range between 0.0475 and 0.0795cm−1atm−1 at 296K. All of our measured self- and hydrogen-shift coefficients are negative and range from −0.002 to −0.008cm−1atm−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 12C16O at room temperature.