Abstract-Terahertz Spectroscopy of 2,4-Dinitrotoluene over a Wide Temperature Range (7–245 K)

Lucia M. Lepodise , Joseph Horvat *, and R. A. Lewis

Institute for Superconducting and Electronic Materials and School of Physics, University of Wollongong, Wollongong, New South Wales 2522, Australia

J. Phys. Chem. A, Article ASAP

DOI: 10.1021/jp5052134

Publication Date (Web): December 16, 2014

Copyright © 2014 American Chemical Society

*E-mail: jhorvat@uow.edu.au. Tel: 61-2-4221 8073.

http://pubs.acs.org/doi/abs/10.1021/jp5052134

Section:

Optical, Electron, and Mass Spectroscopy and Other Related Properties

Previous THz spectroscopy of the TNT explosive precursor, 2,4-dinitrotoluene (DNT), has been restricted to room temperature (apart from one set of data at 11 K). Here, for the first time, we investigate the spectrum as the temperature is systematically varied, from 7 to 245 K. Many new features appear in the spectrum on cooling below room temperature. As well as the five absorption lines observed previously, we observe five additional lines. In addition, a new room-temperature line at 8.52 THz (281 cm–1) is observed. Six of the lines red-shift with temperature and four of them blue-shift. The blue shift is explained by interplay between intramolecular and intermolecular hydrogen bonds. The variation in line width and line intensity with temperature is not systematic, although a conspicuous decrease in line intensity with temperature is observed in all cases. Modeling with hybrid PBE0 and TPSSh functionals helps identify absorption modes.

Abstract-Terahertz Spectroscopy of 2, 4 Dinitrotoluene over a Wide Temperature Range (7-245 K)

Lucia Malebogo Lepodise , Joseph Horvat , and Roger Lewis

J. Phys. Chem. A, Just Accepted Manuscript

DOI: 10.1021/jp5052134

Publication Date (Web): December 16, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/jp5052134

Previous THz spectroscopy of the TNT explosive precursor, 2, 4-dinitrotoluene (DNT), has been restricted to room temperature (apart from one set of data at 11 K). Here, for the first time, we investigate the spectrum as the temperature is systematically varied - from 7 K to 245 K. Many new features appear in the spectrum on cooling below room temperature. As well as the five absorption lines observed previously, we observe five additional lines. In addition, a new room-temperature line at 8.52 THz (281 cm-1) is observed. Six of the lines red-shift with temperature and four of them blue-shift. The blue shift is explained by interplay between intra-molecular and inter-molecular hydrogen bonds. The variation in line width and line intensity with temperature is not systematic, although a conspicuous decrease in line intensity with temperature is observed in all cases. Modeling with hybrid PBE0 and TPSSh functionals helps identify absorption modes.

Abstract-Complementary terahertz absorption and inelastic neutron study of the dynamic anisotropy contribution to zone-center spin waves in a canted antiferromagnet NdFeO3

Evan Constable, D. L. Cortie, Joseph Horvat, R. A. Lewis, Zhenxiang Cheng, Guochu Deng, Shixun Cao, Shujuan Yuan, and Guohong Ma
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.054413

We employ a combination of pulsed- and continuous-wave polarized terahertz spectroscopy techniques to probe temperature-dependent spin waves in the antiferromagnet NdFeO3. Our optical data span 1.6–467 K and reveal a conspicuous spin reorientation between 110 and 170 K, during which the lower-energy mode softens completely. Complementary inelastic neutron scattering reveals that the frequencies of the optically excited spin waves are consistent with a temperature-variable spin gap in the low-energy spin-wave dispersion of NdFeO3. The result links the temperature dependence of the spin waves to a dynamic in-plane anisotropy. The magnetic anisotropy is calculated based on the results of the optical measurements. The change observed in the anisotropy energy along the a and c crystal axes suggests that the spin reorientation evident in NdFeO3 is driven by temperature-dependent in-plane anisotropy.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.054413

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