Absorption Spectrum Studies on the RDX Crystals with Different Granularity in Terahertz Frequency Range

摘要

The absorption spectrum of the cyclotrime-thylenetrinitramine（RDX）with four different particle sizes are measured in the frequency range from 0.1 THz to 2.5 THz by using the terahertz time-domain spectroscopy（THz-TDS）,and the characteristic absorption peaks are acquired.All the samples are measured in a loose condition,which is very close to the real using environment of the RDX.The results show that the four kinds of samples have similar absorption peaks around the frequency of 0.82 THz,1.05THz,1.30 THz,1.46 THz,1.65 THz,and 1.95 THz.The sample with a large particle size obtains more peaks than the small one,while the peaks obtained from the sample with a small size are more protrudent.The reasons for these differences can be the refraction,scattering,and attenuation of the terahertz wave when it passes through the crystal samples.The theoretical terahertz spectrum of RDX was simulated by using density functional calculations,in which,the Becke＆Perdew-Wang’s functional is used in a double numerical plus polarization method（BP/DNP）.Good agreements between the experimental and computed results show that the three peaks located in the frequency of 1.30 THz,1.48 THz,and 1.96 THz are caused respectively by the twisting of three-nitrogen heterocyclic,the symmetrical oscillations of the double nitro groups,and the oscillations of a single nitro group.