Reaction mechanism and kinetics of the NCN+NO reaction: Comparison of theory and experiment

Abstract

The rate constants for the NCN + NO reaction have been measured by laser photolysis/laser-induced fluorescence technique in the temperature range of 254-353 K in the presence of He (40-600 Torr) and N2 (30-528 Torr) buffer gases. The NCN radical was produced from the photodissociation of NCN3 at 193 nm and monitored with a dye laser at 329.01 nm. The reaction was found to be strongly positive-pressure dependent with negative-temperature dependence, as was reported previously. The experimental data could be reasonably accounted for by dual-channel Rice-Ramsperger-Kassel-Marcus calculations based on the predicted potential-energy surface using the modified Gaussian-2 method. The reaction is predicted to occur via weak intermediates, cis- and trans-NCNNO, in the 2A" state which crosses with the 2A' state containing more stable cis- and trans-NCNNO isomers. The high barriers for the fragmentation of these isomers and their trapping in the 2A' state by collisional stabilization give rise to the observed positive-pressure dependence and negative-temperature effect. The predicted energy barrier for the fragmentation of the cis-NCNNO (2A') to CN + N2O also allows us to quantitatively account for the rate constant previously measured for the reverse process CN + N2O --> NCN + NO.

Collisional Relaxation of NCN: An Experimental Study with Laser-Induced Fluorescence

“…These authors observed delayed rise times of the 3 NCN fluorescence signals on the order of 15 μs that were attributed to the mechanism of NCN formation via photolysis of CH 2 N 2 /C 2 N 2 mixtures. Huang et al [31] and Yang et al [32], using the same detection technique but photolysis of NCN 3 at 193 nm as NCN source, did not report any delayed formation of NCN.…”

Quantum chemical treatment of cyanogen azide and its univalent and divalent ionic forms

“…As mentioned in the introduction part, there are some studies concerning the IR spectra of cyanogen azide molecule [12][13][14][15][16][17][18], whereas there is no corresponding study about the charged forms of cyanogen azide molecule in the literature, to the best of our knowledge. Since (to the best of our knowledge), no experimental data are available for the charged forms of cyanogen azide in the literature; we could not compare the calculated IR data with any experimental one.…”

“…According to the experimental and calculated bond length values, the shortest bond length Table 1 Calculated and experimental geometrical parameters of neutral cyanogen azide molecule Ref. [14].…”

“…The calculated and observed values imply that the N2 N3 linkage should have a full -bond but N1 N2 bond, possesses only a partial -bond character. The bond angle constituted by C4 N1 N2 atoms has been calculated as 118 • at UB3LYP/6-31G(d) level (the experimental value was reported as 120 • [35] and 114 • [14]). As it is evident from Table 1, in general there is a good agreement between most of the calculated and observed geometrical parameters of neutral cyanogen azide molecule.…”

“…In that respect, these properties make it an ideal candidate for a quantum chemical investigation. Many experimental data of the neutral molecule exist in the literatures [7][8][9][10][11], especially there are many studies concerning the data of infrared and Raman spectra of it [12][13][14][15][16][17][18]. On the other hand, as far as we know, no report on the univalent and divalent ionic forms of cyanogen azide molecule has appeared in the literature.…”