Methyl Isocyanide: The Low-Frequency Bands ν8 and ν7, and a Determination of the Rotational Constant A0

✍ Scribed by J. Pliva; L.D. Le; J.W.C. Johns; Z. Lu; R.A. Bernheim

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 369 KB
• Volume: 173
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1995.1245

✦ Synopsis

The weak perpendicular bands of the low-frequency fundamental bands (\nu_{8}) and (\nu_{7}) of (\mathrm{CH}{3} \mathrm{NC}) were measured in a long path cell with a high-resolution Fourier transform spectrometer. Analysis of the (v{8}) band shows its origin to be at (\nu_{0}=267.3173 \mathrm{~cm}^{-1}), some (4.3 \mathrm{~cm}^{-1}) higher than previous estimates that were based on an unresolved peak of the bunched-up (Q) branches seen in a lowresolution scan. The (\nu_{1}) band, at (\nu_{0}=1130.6588 \mathrm{~cm}^{-1}), is slightly affected by Fermi resonance with the combination (\nu_{4}+\nu_{8}), whose band is observed just above (\nu_{7}). On combining the observed (\Delta K^{\prime}=+1) transitions of (\nu_{\bar{j}}+\nu_{8}^{-})we reported recently, with the (\Delta K=-1) transitions of (\nu_{\overline{8}}^{-})and of the hot band (\nu_{\bar{\gamma}}+\nu_{8}^{-}-\nu_{8}^{-})accompanying (\nu_{7}), we have been able to obtain accurate values for the ground state rotational constant (A_{0}=5.247234(77) \mathrm{cm}^{-1}) and for the centrifugal distortion constant (D_{k}^{0}=8.5626(24) \times 10^{-5} \mathrm{~cm}^{-1}), which had never been experimentally determined. Accurate spectroscopic constants are also reported for the (\nu_{8}, \nu_{7}), and (\nu_{4}+\nu_{8}) states. ① 1995 Academic Press, Inc.