A study has been made of the hot bands in the ultraviolet absorption spectrum oforthohyphen;xylene and some deuterated derivatives. It is shown that these hot bands arise from excited levels of torsional vibrations of the methyl groups. The spectrum can be explained fairly well assuming independent oscillators with a barrier to internal rotation of 700thinsp;plusmn;thinsp;50 cmminus;1in the ground state and 240thinsp;plusmn;thinsp;35 cmminus;1in the excited state. The origin of the barrier and the applicability of the independent oscillator model are also discussed.
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