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Summary: Chemical Physics 76 (1983) 203-218
North-Holland Publishing Company
LOCAL NORMAL MODES AND VlBRATlONAL ADIABATIC POTENTIALS --
Noam AGMON *
Received 25 January 1982: in final form 3 November 1957
Local normal-mode analysis for a collinear potential energy surface g?nrratss a system of curvilinear coordinaieh. which ;\re
orthogonal in the mass-skewed system. The motion is locally separable in these coordinatrs. We compars the utility ai one of
the normal modes as a transversal-vihralion coordinate. with the convcnrional choicr of the dire&on perpendicular w the
reaction coordinate in the mass-skewed system. The comparison is done for IWOcommonly used reaction coordinates: BEBO
and the steepest-descent path. Results differ for dlfferent choices of directions and reaction conrdinarss. Fururr work ~hcwld
concentrate on a choice of a reaction coordinate which is itself one of the normal modes.
1. Introduction
The assumption of separability of the motion
parallel and transverse to the reaction coordinate
(RC) of a coliinear potential energy surface (PES)
is essential for defining the vibrational frequencies
for the transversal motion. Such an assumption is
usually made at the saddle point in transition state
theory (TST) [l-5], and all along the RC in
evaluating vibrational adiabatic potentials (i.e.
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