Vertical electronic spectra of the isovalent molecules H2CNH, H2SiNH, H2CPH, and H2SiPH on the basis of MRD-CI calculations

Abstract

Large-scale multi-reference single and double-excitation configuration interaction (MRD-CI) calculations are employed for the study of the isovalent compounds H2CNH, H2SiNH, H2CPH, and H2SiPH in their ground state equilibrium geometry. The dipole moments and charge distributions are given. The vertical excitation energies to the intra-valence states 3.1(n, π*) and 3.1(π, π*) and to the first members of the Rydberg series originating from n and π MO's respectively are predicted; the first two ionization potentials and the Rydberg term values are also calculated. In H2CNH, mixing of Rydberg and valence-shell states with CN stretching is analyzed. The trends in relative stability of electronic and ionized states can be directly related to increased orbital stability of n relative to π as soon as a first-row constituent is replaced by a second-row atom. The calculations explain the diffuse character of the uv spectrum of imines; they treat the molecules H2SiNH and H2SiPH for the first time and present a large number of data for all four molecules which can serve as a basis for future experimental investigations on these and related compounds.