Walsh's Rules and the Small Bond Angle States of Triatomic Dihydride Molecules

Abstract

AbstractA series of excited electronic states of AH2 molecules having extremely small bond angles has been discovered theoretically. Systems which have shown this characteristic to date include H2O+, NH2, CH2+, and NH2+. In the present research ab initio studies were carried out using a double zeta plus polarization basis set. Configuration interaction including all Hartree‐Fock interacting single and double excitations was performed. For the 2B2 state of CH2+, the predicted equilibrium geometry is θe(HCH) = 35.2°, re(C‐H) = 1.41 A. This state is bound by 20.3 kcal/mole relative to the separated C+ + H2 ground electronic state. The analogous state of BH2 is not substantially bound, but the neutral C + H2 system shows some very interesting features. All of these results may be qualitatively understood in the context of Walsh's rules.