Spectrum of RDX

Figure 10 ESI mass spectrum of RDX [Reproduced from X. Zhao and J. Yinon, Rapid. Commun. Mass Spectrom., 17 (2003) 943. Copyright 2003, with permission from JohnWiley Sons].

Fig. 10. Laser-induced breakdown spectroscopy (LIBS) spectrum of RDX collected at 20m with ARL standoff LIBS system. The elements present due to RDX are labeled.

Fig. 13.21 shows another example of oscillatory burning of an RDX-AP composite propellant containing 0.40% A1 particles. The combustion pressure chosen for the burning was 4.5 MPa. The DC component trace indicates that the onset of the instability is 0.31 s after ignition, and that the instability lasts for 0.67 s. The pressure instability then suddenly ceases and the pressure returns to the designed pressure of 4.5 MPa. Close examination of the anomalous bandpass-filtered pressure traces reveals that the excited frequencies in the circular port are between 10 kHz and 30 kHz. The AC components below 10 kHz and above 30 kHz are not excited, as shown in Fig. 13.21. The frequency spectrum of the observed combustion instability is shown in Fig. 13.22. Here, the calculated frequency of the standing waves in the rocket motor is shown as a function of the inner diameter of the port and frequency. The sonic speed is assumed to be 1000 m s and I = 0.25 m. The most excited frequency is 25 kHz, followed by 18 kHz and 32 kHz. When the observed frequencies are compared with the calculated acoustic frequencies shown in Fig. 13.23, the dominant frequency is seen to be that of the first radial mode, with possible inclusion of the second and third tangential modes. The increased DC pressure between 0.31 s and 0.67 s is considered to be caused by a velocity-coupled oscillatory combustion. Such a velocity-coupled oscillation tends to induce erosive burning along the port surface. The maximum amplitude of the AC component pressure is 3.67 MPa between 20 kHz and 30 kHz. - ...

In the pressure interval studied, (147-980) 10 newton m", the flame spectrum of NG powder and RDX was continuous except for several lines of the alkali metals. This permitted determination of temperature by optical methods... 

Winstein and coworkers measured the UV spectrum of the homotropenylium ion and showed that its long-wavelength absorption band (/.max 313 nm) was intermediate between that of the tropylium (2max 273.5 nm) and heptatrienyl (/. rdx 470 nm) cations70. Using a Hiickel molecular orbital approach the C(l)—C(7) bond order was estimated to be 0.56. 

Fig. 11. Positive-ion desorption electrospray ionization (DESI) mass spectrum of (a) 10 ng of RDX and (b) 500pg of RDX. Reproduced with permission from Mulligan et al. [23].

Fig. 11. Comparison of laser-induced breakdown spectroscopy (LIBS) spectra of RDX using die double-pulse configuration and the single-pulse configuration. Two 160-mJ pulses were separated by 2jjls for die doublepulse spectrum. One 320-mJ pulse was used to collect die single-pulse spectrum. The O to N intensity ratio for die double pulse and the single pulse is 4 and 2, respectively.

Explosive and Other Properties of R-Salt. Tada (Refs 9 16) studied the effect of neutral salts and of solv effects on the acid decompn of R-Salt. Simecek (Ref 12) reported the treating of R-Salt with AN H2S04 to obtn N, N-Dinitro- A/" nitroso-cyclotrimethylenetriamine which on further treating with the nitrating mixt yielded 98% of RDX. The decompn of R-Salt by coned H SO. was also reported by Simecek (Ref 13). The thermal decompn of R-Salt is the subject of a report by Fowler Tobin (Ref 10) who also detd its IR spectrum Medard Dutour (Ref 11) prepd R-Salt and detd its expl props and some other props in detail. They found R-Salt to be brisant powerful, but easily decompd in the presence of acid Abel s test at 110° - no color to iodine-starch paper in 15 mins... 

Figure 10 The classical power spectrum of a large molecule (RDX, hexahydro-l,3,5-trinitro-1,3,5-triazine) at a very low energy (a) and at its zero-point energy content (78 kcal mol ) (b). Already at the zero point there is extensive classical mode mixing. (Adapted from T. D. Sewell, C. C. Chambers, D. L. Thompson, and R. D. Levine, Chem. Phys. Lett. 208 125 (1993).)...

Studies of the formation of HONO from secondary nitramines, R2N(N02) (R = -CH2-), illustrate an advance made possible by Fast Thermolysis/FTTR methods [I8]. HONO has been considered to be an important intermediate in the thermal decomposition of nitramines [19], but, because of its reactivity, was proposed based on indirect evidence [20,21] until this Fast Thermolysis/FTIR technique was applied. Cis- and trans-HONO are both present in the IR spectrum of the gas from RDX (see the PQR pair at 700-900 cm in Figure 2), but as shown in Figure 3, HONO is transient under the conditions of the experiment. The initial concentration most closely reflects its relationship to the composition of the parent molecule. Figure 4 shows the quantity of HONO as a percentage of the initial gas products for various nitramines [18] versus the H/NO2 ratio in the parent molecule. The general trend suggests that HONO arises from adventitious bimolecular encounters of H and N02 radicals in the condensed phase [18], rather than concerted decomposition of the 4- and 5-center unimolecular intermediates shown below that may contribute in the gas phase [22]. 

We attempted to learn more about the liquid phase of HMX and RDX by recording the FTIR spectrum of rapidly heated samples [57]. The fresh melt of RDX is composed almost entirely of RDX molecules. It requires several seconds before the decomposition products build up to the level where they become detectable by IR spectroscopy. HMX gives evidence of decomposition in advance of melting" and, therefore, we [57] and others [108] prefer to think of HMX as passing into a liquefaction phase because it is no longer a pure material when the solid lattice transits to the molten state. 

The spectrum of the emitted light is characteristic for the atoms, ions, molecular fragments or even clusters of molecules present in the plume of the decomposing explosive. This allows for the detection of short living decomposition intermediates, such as radicals and other reactive species like NO2 or HCN, which are frequently detected as decomposition products of RDX or HMX. 

These are potential explosives. Like RDX and HMX they are thermally stable. But they are more oxygen deficient, therefore they have lower heats of detonation. The Instrument used was a EBQQ type MS/MS (VG 7070 EQ) and was operated in the B/E linked scan mode. An example of a B/E-CID spectrum is shown in Figure 4, which shows the CID spectrum of the molecular ion of compound 6. 

Further reading section for details of Fourier spectroscopy, including its application in NQR. To illustrate the FFT method in pulsed spectroscopy. Figure 5 shows a typical NQR spectrum of powder RDX (C3H O N ), obtained from a free induction decay (FID). 

Figure 5 A typical nitrogen-14 NQR spectrum of powder RDX at 297 K, obtained from a FID. The resonance frequency is -5.193 MHz.

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