Overtone Raman spectrum and molecular polarizability surface of CO2

The Q branches of the Raman bands associated to the 2ν1:4ν02:ν1+2ν02 Fermi resonance of 12C 16O2 have been observed in the gas phase at 2543, 2671, and 2797 cm−1 and, in addition, at 2514 cm−1, one hot band from their first excited vibrational state is seen. From the analysis of their cross sections, jointly with those of the main Fermi diad, ν1:2ν02 and its hot bands, an improved description of the molecular polarizability surface has been achieved. The following derivatives of the mean polarizability have been obtained: ∂ᾱ/∂q1=12.43×10−42 CV−1 m2; ∂2ᾱ/∂q22σ=2.81×10−42 CV−1 m2 (σ=a,b); ∂2ᾱ/∂q21=0.45×10−42 CV−1 m2; ∂2ᾱ/∂q23=0.67 or 0.15×10−42 CV−1 m2; ∂3ᾱ/∂q1∂q22σ=−0.06×10−42 CV−1 m2, in terms of the dimensionless normal coordinates, and ∂ᾱ/∂S1=3.15×10−30 CV−1 m; ∂2ᾱ/∂S22σ=0.36×10−20 CV−1; ∂2ᾱ/∂S21=2.9×10−20 CV−1; ∂2ᾱ/∂S23=2.0 or 0.5×10−20 CV−1; ∂3ᾱ/∂S1∂S22σ=−1.7×10−10 CV−1 m−1, in terms of the symmetry coordinates. The thermal dependence of the mean polarizability is discussed in terms of these quantities.