Spectroscopic study of Λ-doublet, spin, and rotational relaxation in the NH(A 3Π,v=0) state

Abstract

Electronically excited NH(A 3Π) radicals in single N′, J′, e/f states were investigated by pumping on isolated NH(A←X) lines of the (0,0) band. Collision-induced transitions among the different Λ-doublet, spin, and rotational states were monitored by fluorescence spectra. In collisions with NH3, a propensity for conservation of spin is observed. In the original spin unit, rotational relaxation occurs preferably to the neighboring rotational levels. The efficiency of spin-unit changes decrease with increasing ΔΩ. For NH3 collisions inducing a fine-structure change, the rotational distribution is found to be thermal and no memory of the original rotational level is left. In collisions with Ar, spin is not conserved. Generally, relaxation into states of the same Λ-doublet component occurs with approximately the same probability as into the other component. Relaxation processes induced by Ar are less efficient than those caused by collisions with NH3.