Quenching, Λ-doublet mixing and fluorescence lifetimes of single excited NH(A 3Π,v′=0,N′,J′,e/f ) states

Eleven isolated states of NH(A 3Π,v′=0) with selected Λ-doublet, spin and rotational properties were prepared by pulsed laser excitation of ground state NH(X 3Σ−,v″=0,J″) radicals. The average population in both Λ-doublet components was investigated by time resolved fluorescence. Kinetic data for the quenching and collisional Λ-doublet mixing, and fluorescence lifetimes were derived using a simple model. The fluorescence lifetimes for N′=3–8 are found to be independent of rotational excitation in agreement with a recent calculation. The quenching rate constants for collisions with NH3 support the mechanism of complex formation. The mixing of the Λ-doublets induced by collisions with NH3 occurs by dipolar interaction. The kinetics of the mixing by He is in agreement with a recent quantum calculation of inelastic cross sections based on ab initio potential surfaces. Several experiments were performed to characterize the system, particularly the NH(X) precursor.