The pressure dependence of tunnelling of coupled pairs of methyl groups in lithium acetate dihydrate

Abstract

AktracL lhe prssure dependence of tunnelling of mupled pairs of methyl group in lithium acetate dihydrate has been investigated using the wutmn scattering spectrometer IRIS. Methyl tunnelling spctra. recorded at a temperature of 5 K and p u r e s up to 9.5 kbar, rweal SUUcture which has been atlribuled to mupling. The data, which m e n d an earlier invcstigalion by Heidemann d al, have been fitted to a lime-independent Hamiltonian, and the fit parametem include the potential barrien d &e individual methyl groups and the mupling potential between them. The magnitudes of both parameters increase with increasing pressure and their pressure dependence has b x n analyzed to provide information on the inter-molecular foras.the tunnelling spectra could be studied and interpreted as changes were made to both the single-particle and coupling potentials. The experiment was performed as a function of pressure up to 9.5 kbar on the IRIS neutron scattering spectrometer at the pulsed neutron source ISIS, Rutherford-Appleton Laboratory (RAL).

Rotational Tunneling and Neutron Spectroscopy: A Compilation

“…This is about the maximal pressure actually attainable at He temperatures with standard devices. 100 Since deuteration of the rotor also increases (doubles) the scaled potential, it is in this respect equivalent to applying a high pressure to a sample.…”

“…The first spectroscopic proof of the combined coherent counterclockwise tunneling rotation of a onedimensional 3-fold rotor and its center of mass is given for NH 3 adsorbed on a MgO [100] surface. 95 A second example, a Hofmann clathrate, is shown in ref 209, together with a simple mathematical recipe for determining the eigenvalues of eq 27 based on product free rotor wave functions.…”

“…Changes in δℏω t by up to a factor of 3 are observed when applying pressures up to 5 kbars. Examples are presented in refs and −125.…”