Spectroscopy and intensity measurements of the 3ν1+3ν3 tetrad of 12CO2 and 13CO2

Three of the four components of the 3 nu (1) + 3 nu (3) tetrad of (CO2)-C-12-O-16 and (CO2)-C-13-O-16, labeled 30031, 30032, and 30033 in HITRAN notation, have been observed by intracavity laser absorption spectroscopy in the 10 450- to 11 000-cm(-1) region. The rotational analysis has yielded the rovibrational parameters of the vibrational states. The experimental values are found to be in very good agreement with the rovibrational energies recently predicted from variational calculations and reduced effective Hamiltonians. The absolute band intensity of these extremely weak transitions have been measured. The study of the relative intensities within the 3 nu (1) + 3 nu (3) tetrad suggests that part of the oscillator strength is carried by the (22(0)3) state. (C) 2001 Academic Press.