Photoinduced reactions in the Mg[sup +]–NH[sub n](CH[sub 3])[sub 3-n] complex ions: Effect of the methyl substitution.

Photoinduced reactions in Mg[sup +]-NH[sub 2]CH[sub 3] and Mg[sup +] - NH(CH[sub 3])[sub 2] have been studied in the spectral range of 230-440 nm. Although the N-H bond activation channel was found to be prominent in the photodissociation of Mg[sup +] - NH[sub 3] [Yoshida, Okai, and Fuke, Chem. Phys. Lett. 347, 93 (2001)], it is very unfavorable as the ammonia is replaced by methylamines in the complex. Instead, C-H bond cleavage products are observed from Mg[sup +] - NH[sub 2]CH[sub 3](CH[sub 2]NH[sub 2, sup +]) and exclusively produced from Mg[sup +] - NH(CH[sub 3])[sub 2]((CH[sub 3])HN[sup +] = CH[sub 2]) after photoexcitation. For Mg[sup +] - NH[sub 2]CH[sub 3], the C-N bond activation product Mg[sup +]NH[sub 2] and the charge transfer product CH[sub 3]NH[sub 2, sup +] are also abundant. The action spectra of the complexes consist of two pronounced peaks on the red and blue side of the Mg[sup +] 3 ²P ← 3 ²S atomic transition. The calculated absorption spectra of the two complexes using the optimized structures of their ground states are in good agreement with the observed action spectra. On the basis of the branching fraction data and the calculated complex structures, the C-H bond activation is invoked to account for the MgH loss channel after photoexcitation, followed by a nonadiabatic transition to the ground state by a bond-stretch mechanism. However, the formation of Mg[sup +]NH[sub 2] from photodissociation of Mg[sup +] - NH[sub 2]CH[sub 3] involves the insertion of Mg[sup +] into the C-N bond. Finally, the photoinduced charge transfer product CH[sub 3]NH[sub 2, sup +] are also identified from Mg[sup +] - NH[sub 2]CH[sub 3] but not from Mg[sup +] - NH(CH[sub 3])[sub 2]. [ABSTRACT FROM AUTHOR]