SELF-BROADENING AND SELF-SHIFT COEFFICIENTS IN THE FUNDAMENTAL BAND OF 12C 16O

Abstract

High quality and precise measurements of self-broadened and self-shift coefficients in the fundamental band of 12C 16O were made using spectra recorded at room temperature with the high-resolution (0.0027 cm -1) McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectral region under investigation (2008–2247 cm -1) contains the P(31) to R(31) transitions. The data were obtained using a high-purity natural isotopic sample of carbon monoxide and two absorption cells with pathlengths of 4.08 and 9.98 cm, respectively. Various pressures of CO were used, ranging between 0.25 and 201.2 Torr. The results were obtained by analyzing five spectra simultaneously using a multispectrum nonlinear least-squares fitting technique. The self-broadened coefficients ranged from 0.0426(2) cm -1 atm -1 at 296 K to 0.0924(2) cm -1 atm -1 at 296 K, while the pressure-induced shift coefficients varied between −0.0042(3) cm -1 atm -1 at 296 K and +0.0005(1) cm -1 atm -1 at 296 K. The value in parentheses is the estimated uncertainty in units of the last digit. The self-broadened coefficients of lines with same values of m in the P and R branches agree close to within experimental uncertainties while the self-shift coefficients showed considerable variation within and between the two branches. The mean value of the ratios of P branch to R branch self-broadened coefficients was found to be 1.01 with a standard deviation of ±0.01. Comparisons of the results with other published data were made.