Tetraatomic molecules

RENNER-TELLER EFFECT AND SPIN-ORBIT COUPLING IN TRIATOMIC AND TETRAATOMIC MOLECULES... 

H. Beyond the Two-State Renner-Teller Effect TV. Tetraatomic Molecules... 

Appendix A Perturbative Handling of the Renner—Teller Effect and Spin-Orbit Coupling in n Electronic States of Tetraatomic Molecules... 

The complete vibration-rotation Flamiltonian for acetylene-like tetraatomic molecules has been derived by Handy et al. by hand [155] and using a computer algebra program [156]. (Note that in both of the mentioned papers there are some minor errors, see also [144,157,158]). Handy uses as bending coordinates... 

In Section IV.A.4, we show what this general model looks like in the case of H electronic states of symmehic tetraatomic molecules. The situation in H states of asymmetric tetraatomics is briefly discussed in Section IV.B, where we present the handling of a concrete case, the X Uu state of the HCCS radical. For A states the reader is referred to original references [18,149,150,153]. 

Thus only six parameters are required to determine the potentials entering our model for handling the R-T effect in asymmehic tetraatomic molecules... 

We restrict ourselves again to symmetric tetraatomic molecules (ABBA) with linear eqnilibrium geometi7. After integrating over electronic spatial and spin coordinates we obtain for A elecbonic states in the lowest order (quartic) approximation the effective model Hamiltonian H — Hq+ H, which zeroth-order part is given by Eq. (A.4) and the perturbative part of it of the form... 

As in the case of H electronic states of tetraatomic molecules, because of generally high degeneracy of zeroth-order vibronic leves only several particular (but important) coupling cases can be handled efficiently in the framework of the pertnrbation theory. We consider the following paiticnlai" cases ... 

In Chapter XI, Peric and Peyerimhoff discuss the Renner-Teller coupling in triatomic and tetraatomic molecules. For this purpose, they describe some of their theoretical tools to investigate this subject and use the systems FeH2, CNC, and FICCS as adequate examples. 

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