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Ab Initio MRD‐CI Calculations for HAB Molecules I. Isomerization Energies for HOS, HNP and HCSi and Their Positive Ions
Author(s) -
Buenker Robert J.,
Bruna Pablo J.,
Peyerimhoff Sigrid D.
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.198000038
Subject(s) - chemistry , isomerization , ab initio , electronegativity , ion , atom (system on chip) , valence (chemistry) , ab initio quantum chemistry methods , molecule , valence electron , computational chemistry , atomic physics , electron , quantum mechanics , physics , catalysis , biochemistry , organic chemistry , computer science , embedded system
A series of ab initio calculations is reported which employs the MRD‐CI method in a standard AO basis of double‐zeta plus polarization quality for the HSO‐HOS, HPN‐HNP and HSiC‐HCSi isomers and their corresponding positive ions. The equilibrium geometries of each of these twelve systems has been carefully optimized (in some cases in a variety of low‐lying electronic states) and the structural results are found to be in substantial agreement with the qualitative predictions of the Mulliken‐Walsh MO model, although some significant deviations from this general pattern are indicated for certain of the more relatively unstable isomeric species. Unusually large isomerization energies are calculated in a number of instances and a strong preference for structures with the second‐row atom at the terminal position of the molecule is noted generally. The largest and smallest distinctions in the relative stabilities of the isomers studied to date are found to occur for systems with 10 and 12 valence electrons respectively (110 kcal/mole for HCS + ‐HSC + and 2 kcal/mole for ‘A’ HOS + ‐HSO + , for example) and from a survey of such findings it is concluded that each type of molecular orbital exhibits a characteristic effect on the magnitude of these energy differences. Finally it is pointed out that in isovalent series isomerization energies tend to increase with the electronegativity of the second‐row atom in HAB systems of mixed first‐ and second‐row composition.