Knowledge Bank

Air-broadened halfwidth and pressure-induced lineshift coefficients were determined for transitions in the $\nu 3$ fundamental and the $\nu 2+\nu 4,\nu 3+\nu 4$ and $\nu 1+\nu 4$ combination bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ by analyzing room temperature absorption spectra in the 2800 to 3000 and 4136 to $4400cm-1$ spectral regions recorded at $0.01-cm-1$ resolution. In addition, N2-broadened halfwidth and pressure-induced line-shifts were determined for the $\nu 3$ and $\nu 2+\nu 4$ bands. The data were obtained with the McMath Fourier transform spectrometer at the National Solar Observatory on Kitt Peak. A high purity natural sample of methane diluted by dry air or $N2$ to a mixing ratio of -0.01 in a 5 cm to $1.5m$ absorption cell was used to obtain the data. The total gas sample pressures ranged from 60 to 550 Torr. The halfwidth and pressure-shift coefficients were retrieved using a non-linear least-squares curve fitting technique. Determination of the unshifted line positions was improved by fits to spectra of pure methane at low pressures. The vibrational dependence of the retrieved parameters will be discussed by comparing the values with those obtained for similar transitions in other methane bands