Knowledge Bank

The high resolution infrared spectrum of thiophene in the CH-stretch region $(3070-3140cm-1)$ has been observed with a color-center laser spectrometer combined with a pulsed supersonic jet expandion technique. Of 4 fundamental bands $(a1;\nu 1,\nu 2,b1;\nu 12,\nu 13)$ expected in this region, the $\nu 2$ band was analyzed to the confirmation of previous vibrational $assignment.ab$ The rotational constants and band origin were derived from the observed spectra while the ground state constants were fixed at the microwave $values.c$ The $\nu 2$ band was found to be overlapped by an $a1$ vibrational band, which is denoted as $\nu x$. The $\nu x$ band presumably borrows the intensity from the $\nu 2$ band by Fermi resonance. The vibrational assignment of $\nu x$ is not get clear, but the magnitude of the interaction between the $\nu 2$ and $\nu x$ states is calculated to be $0.8cm-1$ from the analysis of the intensity ratio of these bands.