A limit for the quenching of H2(c3π /sub u/) metastables

H2(c3π /sub u/ ) metastables are produced in a pulsed discharge and monitored by absorption of a cw dye laser. The current pulses are ≤5 x 104 A/m2, 300 nsec duration and falltimes of 150 nsec. From the decay of the discharge current and the emission from states of the n=3 manifold, the decay of the metastable excitation is estimated to be 150 nsec. For H2-densities above 4.5 x 1021 m-3 we find that the decay of the metastable absorption signal follows the current and emission signal. This observation yields a lower limit for the quenching rate coefficient of the metastables of 1.5 x 10-15 m3 s-1. Additional measurements of the steady-state absorption at low currents plus the pulsed measurements give a nearly linear dependence on the discharge current density in the range from 30 A/m2 to 105 A/m2. Therefore, quenching of the metastables by electrons can be ruled out as the dominant destruction mechanism