Observation of Photochemical C−N Bond Cleavage in CH₃N₃:  A New Photochemical Route to Cyclic N₃

Abstract

We report VUV-photoionization based photofragmentation-translational spectroscopy data, providing a comprehensive study of the collision free photochemistry of methyl azide (CH3N3) at 193 nm. We report the first observation of the production of methyl and the N3 radical and derive the translational energy release distribution of this reaction. The most probable translation energy is only 8%, and the maximum translational energy is only 60% of the available energy, taking CH3 + linear N3 as the zero of energy. However, the maximum translational energy release is quantitatively consistent with production of the higher energy isomer cyclic N3. Threshold photoionization of the N3 fragment using tunable synchrotron radiation shows results consistent with theoretical predictions of the cyclic N3 ionization potential. The secondary dissociation of N3 --> N(2D) + N2 is also observed and its translational energy release is derived. This distribution peaks at approximately 6 and extends to 11 kcal/mol as would be expected from the size of the exit channel barrier for spin-allowed dissociation of cyclic N3 (7 kcal/mol) and, furthermore, inconsistent with the barrier height of the spin-allowed dissociation of linear N3 (3 kcal/mol). A large fraction (approximately 45%) of the N3 does not dissociate on the microsecond time scale of the experiment suggesting methyl azide may be the most attractive photochemical precursor of cyclic N3 yet found.

The collision-free photochemistry of methyl azide at 157 nm: Mechanism and energy release

“…Although mechanistically complex, the various photochemical channels of methyl azide are easily disentangled with PTS, as has been previously demonstrated. 18,20,21 Our ability to discriminate by time-of-flight (TOF), detected massto-charge ratio, and the synchrotron photon energy, hν synch , allows us to selectively look at all the products, essentially one by one. This greatly simplifies the assignment of the ion signal to its neutral photofragment.…”

“…Rydberg H-atom time-of-flight studies of hydrazoic acid (HN 3 ) photolysis suggest cyclic-N 3 formation, 16,17 and clear evidence is found in the near threshold VUV photoionization-based PTS measurements on methyl azide (CH 3 N 3 ) photodissociation at 193 nm. 18 A complete review is available. 19 Due to both its energetics and dynamics, methyl azide is a potentially interesting precursor for cyclic-N 3 .…”

“…An early study on the photolysis of methyl azide at 248 nm revealed products only from the molecular channel. 20 Later, using a 193-nm radiation, a C-N bond cleavage was observed, 18 but due to the use of VUV photoionization based product detection, it was difficult to derive a reliable branching ratio since the relevant photoionization cross sections were not known. More recently, we have observed both reaction pathways in the 193-nm photolysis of CH 3 N 3 using PTS with EI ionization based product detection.…”

Searching for ways to create energetic materials based on polynitrogen compounds (review)

“…Subsequently, the existence of neutral HEF-N 3 was confirmed in experiments [53] with photolysis of HN 3 containing labeled hydrogen atoms. A very recent experimental study [54] reported on detection of relatively long-living cyclic N 3 species (microsecond lifetime) produced by photochemical decomposition of methyl azide, CH 3 N 3 , irradiated at a wavelength of 196 nm.…”

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

“…A great deal of research has been carried out to assign the microwave, infrared, and electronic spectrum of this moiety [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. As a reactive species, MI can dissociate by 1,2-elimination of H 2 which has been studied both experimentally and theoretically [44][45][46][47][48][49][50][51][52][53][54][55]. Vinylamine and ethyleneimine are chemicals that widely used in industry; they were first detected as primary pyrolysis product of EA in the gas phase using microwave spectroscopic technique by Lovas et al [1,2].…”