Recently, a technique has been demonstrated which allows the measurement of metastable lifetimes in neutral molecules of up to 10(-3) s [J. Chem. Phys. 110, 6319 (1999)]. The present article extends the method by two orders-of-magnitude to molecular lifetimes as long as 10(-1) s. Using the CO metastable a (3)Pi state, lifetimes of eight rovibrational a (3)Pi(upsilon = 3,Ohm,J) levels were measured. Within their experimental error of 30%, these lifetimes agree with previous theoretical predictions [J. Chem. Phys. 110, 6319 (1999)]. The presented technique is suggested for identification of molecular quintet states, in particular the CO a " (5)Pi state. (C) 2000 American Institute of Physics. [S0021-9606(00)00512-2].