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

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.