State-specific lifetime determination of the a 3II state in CO

Abstract

Two different techniques were applied to measure the lifetime of the lowest rotational levels in the metastable a 3II1(ν = 0) state of CO. First, measurement of the absolute absorption cross-section for several absorption lines of the a(ν = 0) ←X (ν = 0) transition yields an Einstein coefficient of A0.0= 97 ± 3 s-1. In combination with the experimentally determined branching ratios for the a→X transition, the lifetime of each component of the a 3II1 (ν = 0,J = 1) A-doublet is determined to be 3.67 ± 0.20 ms. Second, detection of the spin-forbidden fluorescence at two positions in the molecular beam downstream from the excitation region, as a function of velocity of the molecules directly probes the exponential decay. With this technique the lifetime of the lower component of the same a 3II1(ν = 0,J = 1) A-doublet is determined to be 3.4 ± 0.4ms, while for the upper component a value of 3.8 ± 0.5 ms is found. © 1997 American Institute of Physics.