Observation of NH X³Σ^– as a Primary Product of Methylamine Photodissociation: Evidence of Roaming-Mediated Intersystem Crossing?

Abstract

3+1 Resonance-enhanced multiphoton ionization and photofragment excitation spectroscopy have been used to identify NH X(3)Σ(-) as a primary product of methylamine photodissociation after state-specific excitation to the S1 state. On the basis of standard thermochemical data, NH X(3)Σ(-) can be formed only in conjunction with closed-shell CH4 coproducts, indicating that dissociation must occur on the T1 surface. It is proposed that the mechanism for the formation of triplet NH and CH4 involves intramolecular abstraction between frustrated radical products and is an example of roaming-mediated intersystem crossing.

Multi-state pair-density functional theory

“…The potential energy surfaces, dynamics, and spectroscopy of CH 3 NH 2 have been widely studied both experimentally and theoretically. 18,[50][51][52][53][54][55][56][57][58][59][60][61][62][63] Due to the involvement of the conical intersection region in the photodissociation of methylamine, computational methods should be chosen carefully to correctly describe the strong couplings between the electronic states. The ground and rst excited singlet states were studied along four N-H bond dissociation potential energy curves with XMS-PDFT and FMS-PDFT.…”

Evidence for quantum effects in the predissociation of methylamine isotopologues

“…A very appealing system that received considerable interest over recent decades is the prototypical model of methylamine (CH 3 NH 2 ) and its partially, or fully deuterated isotopologues, and particularly their photolysis following excitation to the first UV absorption band. This is due to their similarity with ammonia and relative simplicity, which made them liable to numerous experimental [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and theoretical [28][29][30][31][32][33][34] studies. In particular, five dissociation channels have been discussed and identified, 9,10,[27][28][29][30] including N-H, C-H and C-N bond cleavage that leads to CH 3 + NH 2 , or CH 4 + NH, as well as H 2 elimination from both the amino and methyl groups.…”

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

“…The photochemistry of methylamine after excitation in its first UV absorption band has been the subject of significant experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical [18][19][20][21][22][23][24] attention. Methylamine is the simplest alkyl-substituted analog of ammonia, which provides an almost textbook example of the influence of exit-channel conical intersections on photodissociation dynamics.…”