Physikalisch-Chemisches Institut der Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
J Phys Chem A. 2010 Dec 23;114(50):13011-5. doi: 10.1021/jp107787j. Epub 2010 Nov 23.
We investigated the photodissociation mechanism of N,N-dimethylnitrosamine (CH(3))(2)NNO (DMN) by ab intio quantum chemical methods. Inspired by an earlier study we calculated two-dimensional potential energy surfaces of the S(1) state of DMN in its planar and pyramidal conformations. While the planar molecular geometry appears to possess no direct dissociation channel, the pyramidal configuration is dissociative yielding the products NO + (CH(3))(2)N. Using wave packet dynamics on the planar S(1) potential energy surface the experimental absorption spectrum was well reproduced which gives indirect but strong support for the nondissociative nature of this surface. The transition from the planar to the pyramidal conformation of DMN was then investigated by an ab initio molecular dynamics method which revealed the time evolution of the geometrical parameters of the molecule up to the dissociation of the N-N bond. This occurs about 90 fs after photon excitation. The calculated minimum energy path along the N-N coordinate and the structural changes of the molecule along this coordinate provided a detailed picture of this indirect dissociation or, more specific, predissociation process via conformational change.
我们通过从头算量子化学方法研究了 N,N-二甲基亚硝胺（CH(3))(2)NNO (DMN）的光解机制。受早期研究的启发，我们计算了 DMN 在其平面和三角锥形构象下 S(1)态的二维势能面。虽然平面分子几何形状似乎没有直接的解离通道，但三角锥形构型是解离的，生成产物为 NO + (CH(3))(2)N。在平面 S(1)势能面上使用波包动力学，实验吸收光谱得到了很好的再现，这为该表面的非解离性质提供了间接但有力的支持。然后通过从头算分子动力学方法研究了 DMN 从平面到三角锥形构象的转变，揭示了分子几何参数随时间的演化，直至 N-N 键的解离。这发生在光子激发后约 90 fs。沿着 N-N 坐标计算的最低能量路径以及沿该坐标的分子结构变化提供了这个间接解离或更具体地说，通过构象变化进行预解离过程的详细情况。
