A. Kapur

Ab initio SCF MO calculations of the potential surfaces of thiocarbonyls. II. H2CS, HFCS, CIFCS, and Cl2CS

Potential energy surfaces and equilibrium geometries for the ground and first excited triplet states of H2CS, HFCS, ClFCS, and Cl2CS have been calculated using ab initio SCF MO methods. The triplet state out‐of‐plane bending mode frequencies have been calculated using a perturbation theoretical treatment and a suitable analytic approximation to the potential along the out‐of‐plane bending coordinate. Where experimental results are available, good agreement exists between calculated and experimental data. The equilibrium out‐of‐plane angle in the lowest triplet state is correlated with the decrease in the p electron density on the carbon atom accompanying the change from the planar to the equilibrium out‐of‐plane conformation.

Ab initio SCF MO calculations of the potential surfaces of thiocarbonyls. I. ? 1A1 and ? 3A2 electronic and ? 3A2(b1) vibrational states of F2CS

Ab initio SCF MO calculations using an STO‐3G basis set have been carried out to obtain the potential energy surfaces of the ground ? 1A1 and lowest triplet ? 3A2 states of F2CS. The calculated equilibrium geometry of the ground state is in good agreement with the experimental geometry. Using a suitable analytic approximation to the triplet state potential surface, energies of the stack of triplet state inversion vibrational levels associated with a double minimum potential curve along the out‐of‐plane bending coordinate have been calculated. Good agreement with experiment is obtained.

Abinitio SCF MO calculations of the potential surfaces of thiocarbonyls. III. Ground state and first excited triplet state of thiourea, (NH2)2CS

Equilibrium geometries for the ground and first excited triplet states of thiourea have been calculated using ab initio SCF MO methods. Apart from the pyramidality of the NH2 groups, the calculations for thiourea indicate a planar ground state analogous to simple tetraatomic thiocarbonyls. The first triplet state out‐of‐plane bending mode frequencies have been calculated by a perturbational method. The rotation of the NH2 moiety about the C–N bond has been studied for the ground and first excited triplet states and the barriers to these internal rotations have been calculated.

Calculation of the out-of-plane bending coordinates of tetraatomic molecules by the G-matrix method

Abstract A general expression for the calculation of the G matrix element associated with the out-of-plane bending coordinate of tetraatomic molecules having C2v or Cs equilibrium symmetry is presented. Three methods of calculating the mass weighted out-of-plane bending coordinate as a function of out-of-plane angle are compared.

OUT-OF-PLANE BENDING COORDINATES FOR TETRAATOMIC MOLECULES

Tetraatomic molecules that are planar in their ground states often have pyramidal equilibrium conformations in some of their excited states. For tetraatomic carbonyls and thiocarbonyls (1) some of the excited state out-of-plane angles 8 range from near 0° to more than 40° (2–5), where θ is defined in Figure 1. Out-of-plane bending coordinates have often been described by expressions in which only small deformations are assumed (6) and no specific expressions for molecules having Cs ground state symmetry (with mode 6 as the out-of-plane bending) have been reported.

A NON-EMPIRICAL SCF MO STUDY ON THE GROUND STATE AND FIRST TRIPLET STATE POTENTIAL ENERGY SURFACES OF SIMPLE THIOCARBONYLS

Abstract Simple thiocarbonyls are planar in their electronic ground states but, by anology with the corresponding carbonyls, are expected to be non-planar in their S1 and T1 states.(1,2) Theoretical studies on the excited state geometries of these molecules are of particular interest, since the calculated potential energy surfaces may aid the interpretation of their highly structured T1 ← So and Sl ← So absorption spectra.