Neutron Sciences Directorate

Vibrational spectroscopy is an analytical technique that provides information about molecular structure, chemical bonding, and intermolecular interactions. Infrared absorption and Raman spectroscopies are well-known examples of this widely used form of spectroscopy. VISION uses neutrons rather than photons as a probe of molecular vibrations. This approach has several advantages over optical spectroscopy, including high sensitivity to hydrogen, absence of selection rules, ease of computation of the vibrational spectrum, isotopic sensitivity, no energy deposition in sample, and high neutron penetrability through bulky sample environment. VISION is optimized to characterize molecular vibrations in a wide range of crystalline and disordered materials over a broad energy range (> 5 to < 600 meV). This inverted geometry instrument offers enhanced performance by coupling a white beam of incident neutrons with two banks of seven analyzer modules, equipped with curved pyrolytic graphite crystal analyzer arrays that focus neutrons on a series of small detectors. This arrangement leads to improved signal-to-noise ratio. The overall inelastic count rate is more than two orders of magnitude beyond that of similar spectrometers currently available to users. VISION is equipped with two large diffraction detectors with scattering angles near 90^o and backscattering (Q-range: 1.5 to 30 A^-1) offering good resolution and high count rates. Simultaneous powder diffraction and inelastic scattering provides a detailed description of sample structure and dynamics in suitable samples. VISION offers a variety of sample environments: high pressure, in situ gas adsorption, and low temperatures. Additional capabilities can be developed in collaboration with users. VISION relies on state-of-the-art hardware and software to compute vibrational spectra and assist users with spectral interpretation. Modeling and computational assistance is offered to users, as necessary. The simplicity of the neutron-nucleus interaction permits the easy calculation of the neutron vibrational spectrum: mode frequencies and mode intensities. The similarity of neutron vibrational spectroscopy with its well-known optical counterparts makes VISION an easy-to-use instrument for scientists already familiar with Infrared and Raman spectroscopies.