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The high resolution Hei photoelectron spectra of ethylene and five of its deuterated derivatives (CH2CHD, CH2CD2, cis- and trans-CHDCHD, and CD2CD2) have been recorded and the vibrational bands in the first systems of the molecular ions have been assigned. The anomalous deuterium shifts have been explained by Fermi resonance between ν2 and ν3 levels in CH2CH2 and cis-CHDCHD. The PE spectra of cis- and trans-CHDCHD were found to be different supporting the D2 symmetry of the molecular ion.
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Cvita et al. (1979) studied this question.
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