Asymmetry Parameter. Moments of Inertia. Geometrical Structure

7 Asymmetry Parameter k. Moments of Inertia lx- Geometrical Structure 

According to the rotational constants X = A, B, C given in the preceding chapter, the asymmetry parameter k=(2B - A - C)/(A - C) takes values of about +0.6 and -0.8 for PHg in its observed valence states X and A A,. This shows the radical to be an asymmetric top in the ground state and a near-prolate symmetric top in the excited state. 

The following values for k, Ix, the inertial defect A=Ic - Ib - U ( x and A in amu A ), the inter-nuclear distance r (in A), and the interbond angle a are based on rotational constants derived (from electronic spectra see the preceding chapter) for the vibrational ground states of the indicated species  

Two electronic absorption bands yielded two slightly different sets of parameters. -Correcting earlier data given (with lx and A in g cm units) in [4]. - A very similar set was previously given (with Ix and A in g-cm ) in [5]. 

Approximate interbond angles a (for both observed valence states X and A A,), which were derived from earlier experimental work or from more qualitative theoretical concepts (e.g., the Walsh MO picture), are given In the chapter on the point group, p. 54. Results for the Internuclear distance and the Interbond angle, which were theoretically calculated by ab initio or semlempirical MO methods, are not reported explicitly. Ab initio calculations on r and a of a total of five valence states are in [8], of only the two observed valence states X and A in [9 to 11 ], of only the ground state in [12 to 20] and on a of both X and A in [21 ]. Semiempirical calculations were done on r and a of X [20, 22] and on a of both X and A [23] as well as the ground state X only [24]. 

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