The infrared-driven cis–trans isomerization of nitrous acid HONO III: A mixed quantum–classical simulation
- 作者：Peter Hamm
- 关键词：IR-driven photochemistry ; Matrix spectroscopy ; Mixed quantum– ; classical simulation
- 刊名：Chemical Physics
- 出版年：2008
- 期刊代码：18_03010104
- 类别：ch
- 出版时间：23 May 2008
- 卷：347
- 期：1-3
- 页码：503-513
- 文件大小：1019 K
摘要
A mixed quantum–classical simulation of the IR-driven cis–trans isomerization of HONO in a Kr matrix at 30 K is presented, treating the hydrogen atom as quantum particle and the Kr matrix as well as intermolecular degrees of freedom of the ONO-body as classical. A new method is presented to time-propagate the coupled set of equations in a DVR basis in internal spherical coordinates, rather than in laboratory frame fixed cartesian coordinates. In spherical coordinates, a much more precise computation of the weak vibrational couplings is possible using a still manageable basis size. Good qualitative agreement between simulation and experiment is obtained, underestimating relaxation and isomerization rates by a modest factor ≈5. Upon matrix fluctuations, frequent curve crossings occur between the initially excited OH-stretch vibration and a closely lying combination mode of torsional and bending coordinate that lead to a transfer of population. The subsequent pathway of energy flow is deduced and discussed within a tier model, where trans-states, that belong to the second tier, are populated through a first tier of states that is composed of combinations of bending and torsional excitations. No specific energy pathway is revealed that would funnel the hydrogen atom directly towards the trans-side, hence the experimentally observed high cis → trans quantum yield of close to one probably has to be explained in a statistical scenario on a timescale much longer than that of the present simulation.