Journal of Physical Chemistry B, Vol.123, No.13, 2956-2970, 2019
Computational Study of the Reaction of 1-Methyl-4-amino-1,2,4-triazolium Dicyanamide with NO2: From Reaction Dynamics to Potential Surfaces, Kinetics and Spectroscopy
Direct dynamics trajectories were calculated at the B3LYP/6-31G(d) level of theory in an attempt to understand the reaction of 1-methyl-4-amino-1,2,4-triazolium dicyanamide (MAT(+)DCA(-)) with NO2. The trajectories revealed an extensive intra-ion-pair proton transfer in MAT(+)DCA(-). The reaction pathways of the ensuing HDCA (i.e., HNCNCN) and [MAT(+) - H-C5(+)] (i.e., deprotonated at C5-H of MAT(+)) molecules as well as DCA(-) with NO2 were identified. The reaction of NO2 with HDCA and DCA(-) produces HNC(-ONO)NCN and NCNC(-ONO)N- or NCNCN-NO2-, respectively, whereas that with [MAT(+) - H-C5(+)] results in the formation of 5-O-MAT (i.e., 4-amino-2-methyl-2,4-dihydro-3H-1,2,4-triazo-3-one) + NO and [MAT(+) - H-2(+)] + HNO2. Using trajectories for guidance, structures of intermediates, transition states and products, and the corresponding reaction potential surfaces were elucidated at B3LYP/6-311++ G(d,p). Rice-Ramsperger-Kassel-Marcus (RRKM) theory was utilized to calculate the reaction rates and statistical product branching ratios. A comparison of direct dynamics simulations with RRKM modeling results indicate that the reactions of NO2 with HDCA and DCA(-) are nonstatistical. To validate our computational results, infrared and Raman spectra of MAT(+)DCA(-) and its reaction products with NO2 were calculated using an ionic liquid solvation model. The calculated spectra reproduced the vibrational frequencies detected in an earlier spectroscopic study of MAT(+)DCA(-) droplets with NO2 [Brotton, S. J.; et al. J. Phys. Chem. Lett. 2017, 8, 6053].