Quasilinear molecules

In addition, Winnewisser et al. [36] have demonstrated quantum monodromy for the NCNCS molecule, not only in the (vb, Ka) eigenvalues but also in the Bes = B + C)/2 rotational constant, which varies smoothly with Ka, at fixed Vb for Vb = 0-2, but shows a kink for Vb = 3-5. This observation is a key to the assignment of the extremely congested rotational spectrum of this interesting quasilinear molecule. 

The nature of the monodromy within a given polyad was discussed. Two of the regimes allow no such monodromy one conforms to the type displayed by the swing spring, which has qualitative similarities with that in quasilinear molecules. Finally, the monodromy in the fourth regime is of the folded type, with close qualitative similarities to that observed for LiCN isomerization in Section lllB. 

When C, = 1 the molecule is linear when = 0 is bent. Intermediate cases (such as quasilinear molecules, Bunker, 1983) have 0 < < 1. 

Beyond the early work on acetylene (van Roosmalen et al., 1983a see also van Roosmalen, Benjamin, and Levine, 1984, and Benjamin, van Roosmalen, and Levine, 1984, for the work on the stretch modes), much of the algebraic approach to tetratomic molecules is yet to be fully published. We specifically draw attention to the thesis work of Lemus (1988), which contains important details on the Clebsh-Gordan coefficients of 0(4), and the theses of Viola (1991) and Manini (1991). The formalism necessary to describe linear and quasilinear molecules can be found in Iachello, Oss, and Lemus (1991b) Iachello, Manini, and Oss (1992) and Iachello, Oss, and Viola (1993a,b). See also Bemardes, Hornos, and Homos (1993). 

See, e.g., M. Hargittai, I. Hargittai, Linear, bent, and quasilinear molecules. In Structures and Conformations of Non-rigid Molecules, J. Laane, M. Dakkouri, B. van der Veken, and H. Oberhammer, eds., NATO ASI Series C. Mathematical and Physical Sciences, Vol. 410, pp. 465-489, Kluwer Academic Publishers, Dordrecht, Boston, London, 1993. 

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