The Partition Functions of Molecules with Internal Torsion I. Single Asymmetric Top Attached to Rigid Framework

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Abstract
Crawford's method of treating ``pseudo‐rigid'' molecules is extended to the case involving an asymmetric top. The exact classical kinetic energy for a molecule consisting of a rigid framework to which asymmetric tops are attached is given. From this the quantum‐mechanical operator is derived for the case of one top of small moment of inertia and of small asymmetry. The energy matrix for the molecule is obtained from the operator; and by use of a perturbation method, the partition function for translation, over‐all rotation and internal rotation, correct to the second order, is obtained from the matrix. This includes effects due to translational and angular momentum couplings.