Knowledge Bank

The infrared spectrum of fluorobenzene in the CH-stretch region $(3040-3120cm-1)$ has been observed with a color-center laser spectrometer combined with a pulsed supersonic jet expandion technique. Due to the rotational as well as cooling in the jet, well resolved rovibrational lines were recorded. At least 5 fundamental bands $(a1;\nu 2,\nu 13,\nu 20ab1;\nu 7b,\nu 20b)$ are expected in this region according to the opto-thermal Raman conversion dye laser $spectroscopya$. So far two parallel bands $(v13v20a)$ were analyzed to confirm the vibrational assignments given by the low-resolution spectroscopy. The rotational constants and band origins were derived from the observed spectra assuming those for ground state to the microwave $resultsb,c$. The $\nu 20\mu$ band were found to be overlapped additionally with the two vibrational bands presumably caused by higher order Fermi interaction, whose inertia defects are small negative about $-0.5amu\backslash AA2$. Their vibrational assignments are obscure yet, but the negative inatria defects imply that they include two or four quanta of low frequency out-of-plane vibrational modes such as $\nu 11(\omega =248cm-1)$ and $\nu 16b(498cm-1)$.