Forbidden rotational spectra of polyatomic molecules |
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Authors: | James KG Watson |
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Institution: | Department of Physics, The Ohio State University, Columbus, Ohio 43210 USA |
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Abstract: | Some of the pure rotational transitions of polyatomic molecules that are forbidden according to the rigid rotor selection rules may acquire intensity by a centrifugal distortion mechanism, in which the intensity depends on the dipole derivatives and on the displacements in the normal coordinates produced by centrifugal distortion. The structures of the predicted spectra are discussed for nonpolar molecules belonging to the point groups D3h, Dn (n > 2), D2d, and Td. Some of the calculated R-branch lines of methane are stronger than some of the lines of HD already observed in the same frequency range. For polar molecules extra contributions to the intensity must be considered and are exemplified for the Δk = ±3 transitions of C3v molecules. These forbidden rotational transitions may have some astrophysical importance. |
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