Single-particle rotations in molecular crystals

Abstract

dR ~' d~ P({~,R.},{~,Rj};t) wi'~ E ~ E,Rj})Here P({m~;Rj},{m~;Rj}';t)dj is the density matrix of the molecular crystal. Again the prime in (2.5) means that integration over m~ for j = I should be omitted. 3 Usually it is impossible to handle the above expression and approximations are required, e.g., the replacement of P by a product of single particle density matrices (Hartree approximation /2.9/).

A study of methyl group dynamics and barrier heights in a homologous series of unbranched ketones

“…Principally it consists of a minimum in T 1 which results from the BPP term in equation (1). The precise temperature at which this occurs will depend upon the height of the hindering potential.…”

“…The reasons for this choice have been discussed by a number of authors, as for example in the review by Press and the references cited therein [1]. In particular we focus attention on the property whereby measurements of the CH 3 tunnel splittings at low temperature provide us with accurate values for the magnitude and shape of the potential barrier along with predictions for the hierarchy of torsional states within the barrier.…”

The determination of the effective rotational potential in the plastic phase of C2Cl6from neutron Bragg scattering data

“…This is called the anisotropic crystal field approximation [14]. In crystals which consist of neutral molecules such a monopole-multipole part exists also.…”

Spin-lattice relaxation of deuterated methyl groups: Implications of the pauli principle

“…The Hamiltonian that usually is considered in theoretical treatments of rotational tunneling is given by [2,[20][21][22]:…”

“…Most of this work has, however, dealt with protonated methyl groups. For reviews see the book by Press [2], and the more recent review by Prager and Heidemann [3]. Only in the late eighties workers started to investigate samples containing deuterated methyl groups.…”