Lifetime of the a 3II Metastable State of Carbon Monoxide

Abstract

The rotational dependence of the lifetime of the a ³II metastable state of CO has been investigated using a time‐of‐flight technique. The velocity distribution of metastable molecules is sampled and detected at two positions, 1.9 and 6.7 m from the pulsed electron gun used to excite the ground state molecules effusing from a cooled source slit. The initial population distribution among rotational levels is changed by varying the temperature of the source. A comparison of the number of metastables within given velocity intervals at the two detectors determines the number which decay in flight and yields an experimental plot of the number which decay versus time of flight. A theoretical decay plot is also obtained using the a ³II metastable state lifetimes calculated by James, who predicts rotational level lifetimes ranging from 3 msec to several hundred msec. For two different source temperatures, the experimental and theoretical decay plots are in good agreement.