The infrared spectrum of trimethylenemethane. Predictions of in-plane vibrational frequencies from correlated wave functions

Abstract

The infrared vibrational spectrum of trimethylenemethane (TMM) is predicted with self-consistent field and configuration interaction methods. The 3A′2 electronic ground state of TMM is described in terms of restricted Hartree–Fock theory and in light of experimental evidence. Analytic gradient methods are employed to optimize theoretical geometries for 3A2 TMM; vibrational frequencies are evaluated via analytic second-derivative techniques (self-consistent-field) and finite differences of analytic gradients (configuration interaction). The resulting IR-spectral predictions are modified to reflect average errors statistically associated with the two theoretical methods.