An MPI search for the π→3p Rydberg states of ethylene

A. Gedanken, N. A. Kuebler, M. B. Robin

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Abstract

Two-photon resonances in the 56 000-64 100 cm-1 (1780-1560 Å) region of the multiphoton ionization (MPI) spectra of ethylene-h 4 and -d4 have been observed and interpreted as π→3s excitations, vibronically induced by the torsional modes ν′4 and ν″4. As in the one-photon spectrum, the excitation is rich in ν′2(C=C stretch), and double and quadruple quanta of the ν′4 torsion. An earlier suggestion that π→3p transitions are responsible for anomalies in the π→3s MCD spectrum of ethylene-h4 is not supported by this work, which assigns the anomalies to one-photon π→3s absorptions vibronically induced by a single quantum of ν′4. MPI spectra of ethylene-h4 and -d4 two-photon resonant in the 61 000-71 000 cm-1 region also have been recorded and the vibrational structure analyzed. Prominent electronic origins are found at 62 905 and 66 875 cm-1 in ethylene-h4, and at 63 115 and 67 030 cm -1 in the -d4 compound. These two transitions are assigned as π→3py and π→3px, respectively, where y is in-plane short axis, and x is out-of-plane. As in the π→3s one-photon and two-photon transitions, the two-photon transitions to 3p display long progressions of ν′2 vibrations, each member of which is accompanied by the 2ν′4 and 4ν′4 torsional doublets.

Original languageEnglish
Pages (from-to)46-52
Number of pages7
JournalJournal of Chemical Physics
Volume76
Issue number1
DOIs
StatePublished - 1982

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