Where to look for the electronic spectrum of hydrogen isocyanide, HNC

The geometrical structures and vibrational frequencies of the ground and first excited electronic states of HNC have been predicted by a priori theoretical methods. Using a standard double zeta plus polarization basis set, both the self‐consistent field (SCF) and configuration interaction with all single and double excitations (CISD) levels of theory have been employed. To allow a reasonable assessment of the reliability of the HNC theoretical predictions, analogous studies of the experimentally characterized HCN molecule are also reported. It is hoped that the HNC theoretical predictions will be of assistance in the identification of its electronic spectrum. The HNC electronic spectrum should be distinguishable from that observed by Herzberg and Innes for HCN by: (a) the prediction that the X 1Σ+–A 1A″ energy difference is ∼5000 cm−1 less for HNC than for HCN; (b) for HNC the upper state vibrational frequencies ν2 and ν3 are nearly equal (to within 100 cm−1), while for HCN, the C ≡ N stretch occurs mor...

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