Alr. Bug et Gj. Martyna, Calculation of neutron spectra for hydrogen in zeolites: rotational motions and translational motions in the Born-Oppenheimer limit, CHEM PHYS, 261(1-2), 2000, pp. 89-110
Inelastically scattered neutrons can probe the location and dynamical behav
ior of molecular hydrogen absorbed within zeolites. Hydrogen may, at certai
n temperatures, display mixed quantum/classical dynamics associated with it
s rotational and center-of-mass (CM) motions. When hydrogen diffusion occur
s within a zeolite containing a unique adsorptive site, the spectrum is a s
imple convolution of (quantum) rotational and (classical) CM contributions.
We present a jump diffusion model with a faujasite-type host which illustr
ates this behavior. A more general case would be a host which induces a spa
tially-dependent distribution of rotational frequencies. In order to addres
s this more general situation, we present a formalism in which the standard
time correlation function for neutron intensity:
C(q,t) = [e(i (H) over capt)(b) over cap (q)e(-i (H) over capt)(b) over cap
(dagger)(q)]
is approximated in the "Born-Oppenheimer" limit. A preliminary test of this
formalism is performed for jump diffusion within a one-dimensional model s
ystem. (C) 2000 Elsevier Science B.V. All rights reserved.