Raman and infrared investigations at room temperature of the internal modes behaviour in solid nitromethane‐h₃ and ‐d₃ up to 45 GPa

Abstract

International audienceRaman and infrared spectra of internal phonons in solid nitromethane-h3 and -d3 were measured as a function of pressure in the range 0 – 40 GPa at room temperature. Experiments were performed in diamond anvil cells. The evolution of the splitting of the various modes in condition of nearly hydrostatic compression supports the maintenance of the P21 21 21 crystal structure until the material chemically transforms into an amorphous phase. The observed pressure-induced shifts of vibrational wavenumbers are consistent with computations recently reported in the literature. Infrared and Raman spectroscopies deliver complementary information on the internal modes behaviour. The continuous evolution of the infrared band shapes suggests a weak molecular distortion during the compression process. The strong modifications that are observed in the Raman bands of the nitro group are attributed to polarization effects arising from a rearrangement of the molecules inside the unit cell in the pressure range 10 – 12 GPa, a consequence of a close intermolecular O · · ·H approac

A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane

“…III, it is found that the mentioned modes are from CH 3 and NO 2 stretching modes at ambient conditions and hydrostatic compression shows significant effect on CH 3 and NO 2 groups. A similar behavior has been observed from 9 to 13 GPa in the experiments using Raman measurements [8][9][10] . The variation under pressure of lattice modes are shown in Fig.…”

“…It is insensitive, safe to handle, used as a storable monopropellant and as an additive fuel for combustion engines. Because of its simple crystal structure compared with other secondary explosives, it has been used as a prototype material to understand the energetic materials by both experimentalists [1][2][3][4][5][6][7][8][9][10] and theoreticians. [11][12][13][14][15][16][17] Nitromethane is liquid at room temperature but the molecules condense to form a solid at around 4.2 K. Trivero et al 1 first reported X-rays and neutron diffraction experiments, and found that solid nitromethane crystalizes in an orthorhombic structure in the space group P2 1 2 1 2 1 .…”

Raman spectroscopy of ethane (C2H6) to 120 GPa at 300 K

“…Given that Phase IV has two molecules in the primitive unit cell [4], Davydov splitting is an obvious candidate to explain the splitting in the ν 3 mode commencing immediately upon crystallization and shown both here and in Shimizu et al [3]. Because the Davydov splitting is due to the interaction between the two molecules comprising the unit cell, it is to be expected that the magnitude of the splitting increases with density increase as observed here and also in other systems [18].…”

Recent advances in linear and non‐linear Raman spectroscopy. Part III

“…High-pressure Raman spectra of an L-methionine (C 5 H 11 NO 2 S) crystal for pressures up to 5 GPa were obtained by Lima et al [234] The results show strong modifications of band intensities induced by the applied pressure particularly affecting CO 2 − related bands. Room temperature Raman and infrared investigations of the behaviour of internal modes in solid nitromethane-h 3 and -d 3 up to 45 GPa were performed by Ouillon et al [235] It was concluded that the main part of the observed vibrational changes originates from the weak molecular distortion that occurs during the compression process, without any modification of the crystal symmetry. A highpressure Raman study of alane polymorphs (α-and γ -forms of AlH 3 ) by Tkacz et al [236] revealed a change in the slope of the Raman shift-pressure dependence at a pressure of 8-9 GPa for α-AlH 3 , due to a monoclinic distortion of the initially hexagonal α-AlH 3 , whereas a complete change of the Raman spectrum was observed at pressures of 11-12 GPa for γ -AlH 3 , which points to a structural phase transition from the γ -to the α-phase of AlH 3 .…”