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

Self- and hydrogen-broadening coefficients and pressure-shift coefficients for the first overtone band transitions of <f>12C16O</f> at room temperature have been determined through analysis of nine high-resolution <f>(0.0055 cm−1)</f> 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 <f>(10.0 cm)</f>, the volume mixing ratios of CO in hydrogen were relatively high, <f>∼18</f>–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) <f>12C16O</f> 2-0 transitions by fitting the entire spectral interval from 4130 to <f>4345 cm−1</f> 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 <f>0.0862 cm−1 atm−1</f> at <f>296 K</f> and those of hydrogen-broadening coefficient range between 0.0475 and <f>0.0795 cm−1 atm−1</f> at <f>296 K</f>. All of our measured self- and hydrogen-shift coefficients are negative and range from <f>−0.002</f> to <f>−0.008 cm−1 atm−1</f>. 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 <f>12C16O</f> at room temperature. [Copyright &y& Elsevier]