Doppler-limited dye laser excitation spectrum of the C2 Swan band (v′ − v″ = 1 − 0)

The dye laser excitation spectrum of the Swan band ( v ′ − v ″ = 1 − 0) has been observed with Doppler-limited resolution. The C 2 molecule was generated by the reaction of microwave discharge products of CF 4 with CH 4 . The high sensitivity of laser excitation spectroscopy has enabled us to observe not only ΔΩ = 0 transitions, but also ΔΩ = ± 1 transitions and to determine molecular constants including the spin-orbit coupling constant for both the d 3 Π g and a 3 Π u states. The parameters thus obtained for a 3 Π u were favorably compared with those previously obtained from the Ballik-Ramsay band. The present results on the d 3 Π g v = 1 state were combined with those of an earlier Fourier spectroscopic study on the Swan band ( v ′ − v ″ = 0 − 0) to derive equilibrium molecular constants for the d 3 Π g state. The contributions of the spin-rotation interaction and the centrifugal correction for the spin-orbit coupling to the energy levels in a 3 Π state have been discussed in detail.