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HOT BANDS IN OVERTONE ABSORPTION TRANSITIONS: HIGH TEMPERATURE PHOTOACOUSTIC SPECTRA

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/18506

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Title: HOT BANDS IN OVERTONE ABSORPTION TRANSITIONS: HIGH TEMPERATURE PHOTOACOUSTIC SPECTRA
Creators: Hassoon, S.; Snavely, D. L.
Issue Date: 1993
Abstract: Vibrational overtone hot band spectra are presented. The laser photoacoustic spectra of the $4\nu_{N-H}$ and $4\nu_{C-H}$ overtones of pyrrole, the $5\nu_{C-H}$ of methyl isocyanide and acetonitrile. the $5\nu_{C-H}$ and $6\nu_{C-H}$ of isobutane, and the $6\nu_{C-H}$ of cyclohexane were measured at temperatures up to 140C and compared to the room temperature spectra. Hot bands were identified by their temperature dependence. We observed hot bands in pyrrole, methyl isocyanide and isobutane. From the relative intensities of the hot bands to the main band, the wavenumbers of the thermally populated states were $405 \pm 100, 410 \pm 100$ and $208\pm 100 cm^{-1}$ for pyrrole, isobutane and methyl isocyanide, respectively. These values compare well to the bending motion frequencies in these molecules. A large red shift of the hot bands from the main peak was observed, as expected for high overtone transitions due to the large anharmonicity. The anharmonic constants determined from these shifts are $25cm^{-1}$ for the N-H in pyrrole and $20 cm^{-1}$ for the $C-H$ in methyl isocyanide and cyclohexane. In the case of the $N-H$ absorption the hot band was completely separated from the main transition. In the $C-H$ overtone spectra these hot band absorptions were not separated and result in an apparent increased width of the overtone transition.
URI: http://hdl.handle.net/1811/18506
Other Identifiers: 1993-RB-10
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