State-selective predissociation dynamics of methylamines: the vibronic and HD effects on the conical intersection dynamics.
The photodissociation dynamics of methylamines (CH(3)NH(2) and CD(3)ND(2)) on the first electronically excited state has been investigated using the velocity map ion imaging technique probing the H or D fragment. Two distinct velocity components are found in the H(D) translational energy distribution, implying the existence of two different reaction pathways for the bond dissociation. The high H(D) velocity component with the small internal energy of the radical fragment is ascribed to the N-H(D) fragmentation via the coupling of S(1) to the upper-lying S(2) repulsive potential energy surface along the N-H(D) bond elongation axis. Dissociation on the ground S(0) state prepared via the nonadiabatic dynamics at the conical intersection should be responsible for the slow H(D) fragment. Several S(1) vibronic states of methylamines including the zero-point level and nnu(9) states (n=1, 2, or 3) are exclusively chosen in order to explore the effect of the initial quantum content on the chemical reaction dynamics. The branching ratio of the fast and slow components is found to be sensitive to the initial vibronic state for the N-H bond dissociation of CH(3)NH(2), whereas it is little affected in the N-D dissociation event of CD(3)ND(2). The fast component is found to be more dominant in the translational distribution of D from CD(3)ND(2) than it is in that of H from CH(3)NH(2). The experimental result is discussed with a plausible mechanism of the conical intersection dynamics.
Ahn
Doo-Sik
DS
Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon 305-701, Republic of Korea.
Lee
Jeongmook
J
Choi
Jeong-Mo
JM
Lee
Kyoung-Seok
KS
Baek
Sun Jong
SJ
Lee
Kunhye
K
Baeck
Kyoung-Koo
KK
Kim
Sang Kyu
SK
D003903:Deuterium / Q000737:chemistry*; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry*; D008744:Methylamines / Q000737:chemistry*; D011789:Quantum Theory; D012680:Sensitivity and Specificity; D013499:Surface Properties; D013816:Thermodynamics
D008744:Methylamines; D006859:Hydrogen; D003903:Deuterium