Formation of Rotationally Highly Excited NH (A<SUP>3</SUP> <I>II</I><I><SUB>i</SUB></I>) Radical by VUV Laser at 193nm and Its Reactive Quenching by Foreign Gases

Abstract

NH (A3 IIi) radical has deen produced selectively in the 193 nm laser photolysis of methylamine. Analysis of the rotational population shows non-Boltzmann distribution with its maximum around the levels of N′ = 10. No obvious spin polarization has been observed. The intensity of the (1, 1) vibrational band indicates a low vibrational temperature of this radical.A Stern-Volmer plot of 1/τ(τ; fluorescence life time) versus methylamine p ressure. gives a radiative life time of 545±65 ns for NH (A3 IIi). The slope yields a quenching rate constant of (5.5±0.15) ×10-10cm3·molecule-1. s-1. The quenching constants of NH (A3 IIi) with CO, CH4 C2H4 and CH3OH are very large corresponding to the hard sphere collision rates estimated from the classical theory. It is concluded that the main quenching process is not the spin state conversion of the A3IIi, to a lower singlet state in contrast to the case of NH (c1II) but the formation of reactive intermediates with those gases.