Laser Stark spectroscopy of carbon dioxide in a molecular beam

Laser Stark spectroscopy has been performed for CO₂ molecules in a bolometrically detected supersonic beam, using a tunable infrared F-center laser to excite rovibrational transitions in the 3715-cm^-1 "ν₁ + ν₃" band of ¹²C¹⁶O₂. The very weak Stark effect of CO₂ is amply resolved by realizing an effective spectroscopic linewidth of 2 MHz and by using uniform electric field strengths in excess of 200 kV cm^-1. Stark spectra for the R(0) and P(2) transitions enable evaluation of the isotropic part (α_n) and anisotropy (Δα_n) of the static molecular polarizability in both excited (n = v) and ground (n = 0) vibrational states. Direct observables are Δα_v Δα₀ = 1.021(8); (α_v - α₀) Δα_v = 0.012(6); Δα_v = 2.65(18) A ̊³, the last result being 12% greater than predicted. The results test the relative magnitudes of electronic and vibrational contributions to the static polarizability and indicate the way in which the polarizability tensor varies from one vibrational state to another.