Vibrationally induced formation of NaH in the Na(3p)+H2 collision system:: Rate equation model and comparison with experimental results

Nonlinear optical methods (four-wave-mixing spectroscopy) and linear absorption spectroscopy were used to analyze the reaction of sodium hydride (NaH) in the Na(3p)+ H-2 collision system.-To explain the reaction pathway, we developed a rate equation model which reproduced the dynamic and kinetic behavior of the Na(3p)+ H-2 system at all parameter values chosen in the cell experiment. The concentration of the reactants was varied and different excitation lasers with short (10 ns) and long (1.5 mu s) pulses were used. The model describes the chemical formation of NaH by the following two-step process: (I) Na(3p)+ H-2-->Na(3s)+ H-2(upsilon ">0), and (II) Na(3p)+ H-2(upsilon ">0) --> NaH+H. The rate constant of the final step, which represents a collision of a Na(3p) atom with a vibrationally excited H-2 molecule (upsilon ">0), is determined for the first time as k = (1.1 +/- 0.3) x 10(-9) cm(3) s(-1). (C) 1998 American Institute of Physics.