VISION and VirtuES: High throughput Inelastic Neutron Scattering Spectrometer with dedicated computer modeling resources

Anibal J (Timmy) Ramirez-Cuesta
Chemical and Engineering Materials Division, NScD, ORNL

Abstract

Molecular spectroscopy is a very powerful tool to study the dynamical properties of solid, liquid and gases. Inelastic Neutron scattering is a very powerful tool to study hydrogen-containing materials. With the development of neutron spallation sources, and the use of epithermal neutrons, inelastic neutron scattering can measure the vibrational spectra of materials on the whole range of vibrational motions (0-4400 cm^-1) and effectively opening the field of neutron spectroscopy [1]. INS is a technique that was mostly used to study hydrogen-containing materials due to the high cross section of hydrogen [2]. 

The recently commissioned VISION spectrometer at the SNS in Oak Ridge Tennessee has an increased overall flux at low energy transfers up to 4000 times over its predecessors and it has unprecedented sensitivity. From the determination of INS spectra of publishable quality in minutes (for samples in the gram quantity range) [3], measuring the signal of samples in the milligram range to the direct determination of the signal of 2 mmol of C0₂ adsorbed on functionalized catalysts [4]. 

Sample environment developments are a crucial part of an effective neutron scattering program, at VISION we have developed the world's largest single crystal diamond anvil cell and measured the INS spectra of 1 mm³ of a HMB sample. Gas handling experiments are trivial to perform. A sample changer designed for VISION is available, it is a whole new concept that will allow continuous operation for large number of samples (hundreds at a time) that will enhance the mail-in program for sample measurement. Recently, a simultaneous Raman and INS center-stick has been developed and tested in VISION measuring simultaneously the rotational spectra of hydrogen in the gas, liquid and in the solid state as function of the relative para-ortho hydrogen concentrations. 

Finally, the major challenges that we are facing will be discussed, in particular methods to automate data analysis and interpretation through computer modelling [5]. We have computer cluster: VirtuES (VIRTUal Experiments in Spectroscopy) dedicated to analyse VISION data. We are also developing ICEMAN (Integrated Computer Environment; Modeling and Analysis for Neutron data) a new software to simplify the link between computer modelling and neutron scattering data and maximise the benefits of the VirtuES cluster.

References

[1] Mitchell PCH, Parker SF, Ramirez-Cuesta A, Tomkinson J. Vibrational Spectroscopy with Neutrons, with applications in Chemistry, Biology, Materials Science and Catalysis. London: World Scientific; 2005. 
[2] AJ Ramirez-Cuesta, MO Jones, WIF David, Materials Today, 12, 2009, 54-61. 
[3] Jalarvo, N., Gourdon, O., Ehlers, G., Tyagi, M., Kumar, S. K., Dobbs, K. D., . Crawford, M. K. (2014). The Journal of Physical Chemistry C, 118(10), 5579.5592. doi:10.1021/jp412228r 
[4] T. J. Bandosz, M. Seredych, E. Rodriguez-Castellon, Y. Cheng, L. L. Daemen, and A. J. Ramirez-Cuesta, Carbon 96, 856 (2016). 
[5] M. E. Casco, Y. Q. Cheng, L. L. Daemen, D. Fairen-Jimenez, E. V. Ramos-Fernandez, A. J. Ramirez-Cuesta, and J. Silvestre-Albero, Chem. Commun. 52, 3639 (2016).