Horace R. Danner

Low‐frequency molecular vibrations in solid n ‐paraffins by neutron inelastic scattering: n ‐Pentane, n ‐hexane, n ‐heptane, and n ‐octane

The torsional and skeletal bending fundamentals in solid n ‐pentane, n ‐hexane, n ‐heptane, and n ‐octane are measured by the method of cold neutron inelastic scattering. For this series of n ‐paraffins, the maximum frequencies of the skeletal torsion and skeletal bending modes approach 190 and 500 cm−1, respectively, in agreement with previous measurements on polyethylene. The average frequency of the two end‐methyl torsions is found to be 240 cm−1. A normal coordinate analysis, performed using only intramolecular valence force fields for each molecule, is used as a guide in spectral assignments. These results are compared to theoretical dispersion curves of polyethylene, with and without intermolecular forces. Chain‐end effects appear to be of little significance for these low‐frequency modes, even in chain lengths as short as seven or eight carbons.

Lattice vibrations of a monolayer of n‐butane adsorbed on graphite

The incoherent inelastic neutron spectrum of a monolayer of n‐butane adsorbed on graphite has been analyzed. The system corresponds to a two‐dimensional lattice with a unit cell having one n‐butane molecule and four substrate atoms of infinite mass. The potential energy matrix for the vibration is set up in Cartesian coordinates with both intramolecular valence force fields and intermolecular pairwise potentials. The calculated frequency dispersions and hydrogen amplitudes are used to calculate the neutron scattering cross sections. They are summed for all normal modes and folded with both the instrumental resolution function and the incident beam profile to form a composite time‐of‐flight spectrum. The comparison of the calculated spectrum with observation provides a set of intermolecular force constants. The best agreement is obtained with the hydrogen–substrate and the hydrogen–hydrogen constants of 0.04 and 0.003 mdyn/A, respectively.

Sinusoidal modulation for a neutron Fourier TOF spectrometer

Abstract Sinusoidal modulation for neutron time-of-flight measurements is obtained using a stator with specially shaped windows.

Low frequency skeletal vibrations and rotational isomers of solid 1,4-dibromobutane and 1,5-dibromopentane studied by neutron inelastic scattering

Abstract The neutron inelastic spectra of solid 1,4-dibromobutane and 1,5-dibromopentane have been taken at several temperatures. The observed neutron spectra are assigned to the skeletal bending and torsion modes on the basis of normal coordinate calculations, in which only intramolecular valence force fields are used. The spectral assignments are consistent with the GG conformer being the predominant species in solid 1,4-dibromobutane while the TT conformer is predominant in 1,5-dibromopentane; lesser amounts of the TT isomer in the former and the GG isomer in the latter have also been identified.

Low frequency skeletal vibrations in solid n-alkyl bromides by neutron inelastic scattering: n-pentyl, n-hexyl, n-heptyl and n-octyl bromides

Abstract The skeletal bending and torsional fundamentals in solid n -pentyl, n -hexyl, n -heptyl and n -octyl bromides are measured by the technique of cold neutron inelastic scattering. The observed frequencies are assigned on the basis of normal coordinate calculations using simplified valence force fields. The frequencies of the end-methyl torsion were observed about 240 cm −1 , virtually unchanged from that of n -paraffins. The observed and calculated data were correlated with ν 5 and ν 9 dispersion curves of polymethylene by making suitable phase-difference assignments.