Articles written in Journal of Chemical Sciences
Volume 104 Issue 6 December 1992 pp 629-633
The application of supersonic jet spectroscopy to the study of low-frequency, large-amplitude, anharmonic motions in the excited states of floppy molecules has been discussed. In particular, our work on inversion and torsional vibrations of 9, 10-dihydroanthracene and dihydrophenanthrene by laser-induced fluorescence excitation technique has been reviewed. The inversion of dihydroanthracene is nicely fitted with a quadratic Gaussian type potential function and the height of the barrier in the S1 state is calculated to be 94 cm−1. The inter-ring torsional frequencies of dihydrophenanthrene appear as a prominent progression and Frank-Condon analysis shows that the S1 state of the molecule is planar in contrast to a skew configuration in the ground state. A peculiar alternation of band gaps has been noticed.
Volume 114 Issue 6 December 2002 pp 623-638
This paper presents the evolution of views on methyl internal rotation potential barrier. Various mechanisms proposed for the origin of torsional barrier in ethane have been reviewed. Inadequacy of one dimensional description of internal rotation has been highlighted in small methyl conjugated molecules in the light of its multidimensional nature. The effect of skeletal flexing on the picture of barrier formation by dissecting the barrier energy into potential type, virial type and symmetry type is described. The role of π and σ electrons at different stages of molecular flexing is discussed. The analysis identifies the dominant contributions to barrier origin as π-bonding changes during rigid rotation and σ-bonding changes resulting from bond lengthening during methyl group rotation. The contribution of lone pair electrons in determining the preferred structure of the methyl group in imine compounds such as 1-methyl 2-(1H)-pyridinimine is presented.
Volume 134, 2022
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