Reactive Collision Dynamics of the Collision System Mg + H2 Using Far Wing Laser Scattering

The far wing absorption of laser light to the collision complex MgH2 leads to nonreactive formation of excited state magnesium, Mg*, and reactive formation of MgH [1]. Far wing absorption of laser light is monitored by observation of the final product (Mg* or MgH) as a function of pump laser detuning from the magnesium resonance line. We monitor production of MgH (v″ = 0) rotational levels J″ = 6 and J″ = 23, close to low J and high J maxima of a bimodal rotational distribution, respectively. For this we use laser-induced fluorescence in a two laser pump and probe experiment. We also monitor the competing nonreactive channel Mg* by observation of resonance fluorescence Mg (31P 1 0 - 31S0). The onset of the reactive channel in the Mg + H2 system is highlighted through a comparison with far wing profiles from the nonreactive collision system Mg + H2 and the reactive system Mg + H2 [1]. We have developed a simple excited state dynamics model for the theoretical interpretation of our data. This model uses standard quasistatic theory to estimate the absorption probability as a function of detuning of the laser frequency from resonance. The potential energy curve data [2] is limited to fixed geometries, C2v and C∞v. Based on this, only rough comparisons are possible between the dynamics model and experiment.