Multispectrum Analysis of the v4 Band of CH3CN: Positions, Intensities, Self and N2 Broadening and Pressure-Induced Shifts
A multispectrum nonlinear least squares fitting technique has been applied to measure accurate zero-pressure line center positions, Lorentz self- and N2-broadening coefficients and self- and N2-pressure-induced shift coefficients in the parallel ν4 band of CH3CN near 920 cm-1. Fifteen high-resolution (0.0029 cm-1) laboratory absorption spectra of pure and N2-broadened CH3CN recorded at room temperature using the Bruker IFS 125HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, U.S.A. were analyzed simultaneously. Short spectral intervals containing manifolds of transitions from the same value of J have been fitted together. In all, we have obtained high precision line positions, absolute line intensities, self- and N2-broadening coefficients for P(44) through P(3) and R(0) through R(46) manifolds. All measurements have been fitted successfully assuming a Voigt line shape. Preliminary fits of line intensities up to J = 47 using one principal dipole moment derivative and three Herman-Wallis terms are reported. The results are not fully satisfactory due to perturbations caused by interactions with other bands. The total intensity obtained from this prediction by summing individual line intensities for the v4 band region has been compared with the integrated absorption coefficient reported for the v4 band from lower resolution spectra measured at the same laboratory facility. The variations of N2 broadening, self-broadening, N2- shift and self-shift coefficients with the J and K quantum numbers have been measured for the first time. N2-broadening coefficients decrease with increasing J and K. Some self-broadening coefficients are very large (up to ~2 cm-1 atm-1 at 294 K). Ratios of N2-broadening coefficients to self-broadening coefficients show a compact distribution with rotational quantum number in both the P- and R-branches that range from ~0.45 to 15 with a maxima ratio near J"=13. Pressure-induced shifts for N2 are small (few exceed ±0.006 cm-1 atm-1 at 294 K). In contrast, self-shift coefficients are large (maxima of about ±0.06 cm-1 atm-1) and are both positive and negative with compact and distributions as a function of rotational quantum number. A calculation of the total internal partition function sum has been performed and those results have been made available for addition to the HITRAN and GEISA databases. We discuss the status of assignments for CH3CN that are currently available for other mid- and far infrared regions
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 927709
- Report Number(s):
- PNNL-SA-58205; JQSRAE; 400409900; TRN: US200816%%1170
- Journal Information:
- Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 109, Issue 6; ISSN 0022-4073
- Publisher:
- Elsevier
- Country of Publication:
- United States
- Language:
- English
Similar Records
Multispectrum analysis of the v9 band of 12C2H6: Positions, intensities, self- and N2-broadened half-width coefficients
A Multispectrum Analysis of the v1 Band of H12C14N: Part II: Air- and N2-Broadening, Shifts and Their Temperature Dependences