15min:

MARY ANN H. SMITH, Science Directorate, NASA Langley Research Center, MS 401A, Hampton, VA 23681-2199; D. CHRIS BENNER AND V. MALATHY DEVI, Department of Physics, The College of William and Mary, Williamsburg, VA 23187-8795.

Self- and air-broadened halfwidth and pressure-induced shift coefficients and their temperature dependences have been determined for a number of transitions in the ₄ and ₂ bands of ¹²CH₄ from laboratory absorption spectra recorded at room temperature and below with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory. In addition, accurate line center positions and absolute intensities were determined. The results were obtained by using a multispectrum nonlinear least squares technique to fit simultaneously 20 or more spectra recorded at high resolution (0.006-0.01 cm^-1) with path lengths between 1 and 150 cm and sample temperatures ranging from 210 to 314 K. For both self- and air broadening in the J-manifolds of the P and R branches of the ₄ band, we observed line mixing between certain transitions within the same manifold. In these cases the off-diagonal relaxation matrix elements were determined in the fits. Most of the air-broadened widths of unmixed ₄ lines retrieved using the multispectrum fits agree well with earlier values determined from single-spectrum fits, and the multispectrum results have smaller statistical uncertainties. The inclusion of line mixing in the fits was seen to have a greater effect on the retrieved values of the line shifts than on the retrieved values of other parameters.