Henry A. Havel

A computer algorithm for the convenient normal-coordinate analysis of molecules with redundant coordinates

Abstract The traditional way of handling the vibrational problem in molecules with redundant internal coordinates becomes algebraically cumbersome when applied to larger molecules. The problem is much simpler when transformed into Cartesian coordinates since there are no redundancies in this space. This transformation is, however, nonlinear and therefore the linear internal-coordinate force constants contribute to the quadratic Cartesian ones and must be included. If the linear internal-coordinate force constants are known in advance, the solution of the normal-coordinate problem in Cartesian space is straightforward. This, unfortunately, is seldom the case. A new algorithm is proposed which allows the linear internal-coordinate force constants to be determined from a knowledge that the equilibrium configuration corresponds to a total minimum in the potential energy and a number of additional constraints equal to the number of redundant internal coordinates. This algebraically simple algorithm is shown to be fully equivalent to the more conventional ones.

A Vibrational Rotational Strength of Extraordinary Intensity. Azidomethemoglobin A

The asymmetric stretching vibration of the N3 - group in azidomethemoglobin A (azidometHb A) exhibits a vibrational circular dichroism (VCD) band (Fig. 1) of extraordinary and unprecedented intensity. Its rotational strength is three orders of magnitude greater than any heretofore noted. Integration of the VCD band gives a vibrational rotational strength (per tetramer) of 3 × 10 -40 (esu cm)2, a value typical for the electronic rotational strengths associated with the n → π* transition in saturated ketones.

The charge flow model applied to the vibrational circular dichroism of oriented species

Abstract The charge flow model is applied to the vibrational circular dichroism associated with oriented species. Expressions are derived for the three rotational strengths associated with light propagating along three orthogonal axes. The relevance of these expressions for the determination of the vibrational electric quadrupole transition moment is discussed.