We reanalyze the theoretical lifetimes of the metastable a (3)Pi (v=0,Omega
,J) levels as well as the spontaneous a (3)Pi(v = 0) decay rates into the X
(1)Sigma(+) (v) ground state levels, clearly favoring the measurements of
Jongma et al. [J. Chem. Phys. 107, 7034 (1997)] as compared to the theoreti
cal results of James [J. Chem. Phys. 55, 4118 (1971)]. Theoretical lifetime
s of the vibrationally higher lying metastable levels a (3)Pi (v=1-3,Omega,
J) are listed for the first time. The lifetimes of the two Lambda component
s are shown to be different. A new technique for measuring the lifetime of
individual rovibrational metastable molecular levels is applied to the CO r
ovibrational level a (3)Pi (v = 3,Omega =1,J=2). Our result tau=3.04+/-0.38
ms is in good agreement with the theoretical lifetime of 2.97 ms. The meta
stable population is deduced to be N-meta =(2.3+/-1.2) . 10(6) molecules/sh
ot. Finally, our ms lifetime measurement technique is compared with that de
veloped by Jongma et al. [J. Chem. Phys. 107, 7034 (1997)]. (C) 1999 Americ
an Institute of Physics. [S0021-9606(99)00313-X].