A neutron-diffraction study of liquid acetonitrile

Abstract

Neutron-diffraction studies on liquid deuterated acetonitrile at 20~C were carried out at neutron wavelengths of 0"5 A and 0.7 A.. For the latter wavelength samples of two different diameters were measured.The data were corrected for background, absorption, multiple scattering and inelastic effects (Placzek correction) and then were normalized to absolute differential cross section by comparison with vanadium standard. The different steps in the correction procedure were experimentally verified.The absolute coherent distinct differential cross section was separated into intermolecular and intramolecular contributions. The variation of molecular structure in passing from the gas phase to the liquid was obtained from this intramolecular contribution. INTRODUCTIONIn molecular liquids as opposed to simple atomic liquids non-central forces are generally important [1] and this results in more complicated expressions for molecular correlation functions which are needed in statistical calculations of thermodynamic properties of liquids. The pair-correlation function which plays a central role within the pair theory of liquids depends for molecules not only on the separation between molecules but also on their relative orientations [2][3][4]. This molecular pair-correlation function may in principle be determined from diffraction experiments [5] but a large number of different experimental data from neutron diffraction using different isotopes and X-ray diffraction are required.The present investigation was carried out in order to provide as much diffraction data as possible for one molecular liquid. Acetonitrile was chosen since X-ray data are already available [6] and at least two different neutrondiffraction studies on the isotopes CD3C14N and CD3CISN are feasible. In the present paper data for CDaCI~N are presented, whereas results for CD3CISN will be published in a second part of this series.Acetonitrile seems to be quite an appropriate example to study. Its large electric dipole moment of 3-92 D t and its comparatively high boiling point indicate strong non-central intermolecular forces and preliminary interpretations of the X-ray data [6] seem to favour strong orientational correlations. On the other hand, the acetonitrile molecule possesses structural symmetry which facilitates evaluation of the molecular pair-correlation function [2] and also its gasphase structure is well established [7][8][9].

The Molecular Structure and Hydrogen Bond Geometry in Liquid Formamide: Electron, Neutron, and X-Ray Diffraction Studies

“…The data were converted to an absolute scale by determining a normalization factor from a vanadium run. The details of the correction procedure are described elsewhere [12][13][14], X-ray diffraction measurements were carried out on flat plane-parallel specimens using transmission The details of the data processing and correction procedure are discussed in [15].…”

“…where /nom\{k), /"elf (k), f*{k) are respectively the normalized coherent intensities, calculated self scattering of the atoms in one formamide molecule and tabulated [14][15][16][17] coherent scattering amplitudes for atoms /. Index a stands for the three different types of diffraction experiments.…”

“…Index a stands for the three different types of diffraction experiments. A final correction to eliminate systematic errors, arising from inaccuracies in correction, was applied to the experimental structure functions [11][12],…”

Microscopic structure of Fe-Ni and Fe-Ni-S molten alloys of geophysical interest

“…The intensity for the empty furnace and a cadmium neutron-absorbing rod of similar diameter to the sample were also measured to account for the effect of sample self-shielding on the background count rate at small scattering angles. 17 Each complete diffraction pattern was built up from the intensities measured for the different detector groups. These intensities were saved at regular intervals and no deviation between them was observed, apart from the expected statistical variations, which verified the diffractometer and sample stability.…”

The Molecular Conformations and Intermolecular Correlations in Positional Isomers 1- and 2- Propanols in Liquid State Through Neutron Diffraction

“…(6a) beyond q = q max is almost zero. Again, the function G d (r) is expected to be zero in the range 0 ≤ r ≤ r 0 where r 0 is about 1.5 Å because (Bertagnolli et al, 1976) for neutron data analysis of liquid acetonitrile.…”