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Walsh's Rules and the Small Bond Angle States of Triatomic Dihydride Molecules
Author(s) -
Casida Mark E.,
Chen Maynard M. L.,
Macgregor Robert D.,
Schaefer Henry F.
Publication year - 1980
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198000012
Subject(s) - chemistry , triatomic molecule , ab initio , excited state , bond length , atomic physics , basis set , ground state , molecular geometry , molecule , electronic correlation , context (archaeology) , ab initio quantum chemistry methods , computational chemistry , crystallography , density functional theory , physics , paleontology , organic chemistry , biology
A series of excited electronic states of AH 2 molecules having extremely small bond angles has been discovered theoretically. Systems which have shown this characteristic to date include H 2 O + , NH 2 , CH 2 + , and NH 2 + . 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 2 B 2 state of CH 2 + , the predicted equilibrium geometry is θ e (HCH) = 35.2°, r e (C‐H) = 1.41 A. This state is bound by 20.3 kcal/mole relative to the separated C + + H 2 ground electronic state. The analogous state of BH 2 is not substantially bound, but the neutral C + H 2 system shows some very interesting features. All of these results may be qualitatively understood in the context of Walsh's rules.