Infrared spectroscopy of short-lived molecules

The method of laser electric resonance has been applied to the observation of the ν2 fundamental band of the HCO radical using 12C16O2 and 12C18O2 infrared laser lines. Forty-three resonances have been assigned to six low-J vibration-rotation transitions, qQ1(1), qP1(2), qR1(1), qQ2(2), qP2(3), and qR2(2), each having spin-rotation splitting and K-doubling. The resonances have been analyzed using the detailed theory of the Stark effect in doublet electronic states of asymmetric top molecules. Using previous microwave values for the parameters in the ground state of HCO, the following constants have been determined: ν 0 +4(Δ′ K − Δ″ K ) = 1080.8392(16) cm −1 , A′ − A″ −5(Δ′ K − Δ″ K ) = 2.15146(42) cm −1 , B′ + C′= 2.89259(60) cm −1 , B′ − C′= 0.10572(105) cm −1 , ϵ″ aa = 0.3885(30) cm −1 , ϵ′ aa = 0.4701(36) cm −1 , η″ aaaa = −0.0016(10) cm −1 , η′ aaaa = −0.0018(13) cm −1 , μ″ a = 1.3626(39) debye , μ′ a = 1.3474(48) debye . The variation of the molecular constants with excitation of the ν2 vibration and the relative merits of electric and magnetic resonance methods are discussed.