Spectral distribution of CO2 vibrational states produced by collisions with fast hydrogen atoms from laser photolysis of HBra)

193 nm photofragmentation of HBr molecules in HBr/CO₂ mixtures produces energetic (∼2.5 eV) hydrogen atoms which vibrationally excite CO₂ molecules via an inelastic translation-vibration/rotation (T-V/R) energy exchange process. Prompt infrared emission in the 4.3 μm region has been wavelength resolved, and the spectral energy distribution associated with the excited CO₂ product was measured. The emission profile is strongly red shifted from the spectral region of the ν₃ (00⁰1-00⁰0) fundamental transition indicating that these energetic collisions preferentially produce combination and overtone levels with oscillator strength in the 4.3 μm region. Cold gas filter studies show that significant emission originates from CO₂ bend-stretch excitation compared to pure stretching excitation. Approximately 15% of the emission is due to the 01¹1-01¹0 transition while the remaining fluorescence has contributions from levels above the 01¹1 state. The data are in qualitative agreement with theoretical calculations on O/CO₂ collisions employing either quasiclassical trajectory or infinite order sudden methods, but do not agree with predictions based upon either (harmonic oscillator) breathing sphere theory or statistical theory.