A study of the near infrared emission bands of the hydroperoxyl radical at medium resolution

Emissions of the hydroperoxyl radical HO₂ in the spectral range from 1.0 to 1.6 μm were studied at low and medium resolution. The resolved spectrum shows the expected parallel band structure for the vibrational ovetone transition ²A″ (200-000); in the case of the vibronic transitions ²A′, 000 → ²A″, 000 and ²A′, 001 → ²A″, 000, however, comparison of experimental and computer simulated spectra shows that there also occur intense subbands with ΔK = 0, in addition to the ordinary ΔK = ± 1 transitions. The cause for the break-down of the type-C selection rule is not well known. In the reaction system of ethylene with discharged oxygen vibronic bands could be observed originating from ²A′ levels up to at least ν′₃ = 6. The most probable excitation mechanism for these high vibronic levels is the chemiluminescent reaction HCO + O₂ (¹Δ_g) → HO₂(²A′, 00ν′₂) + CO. From the computer fits to the spectra of HO₂ and DO₂ at medium resolution the origins of the 000-000 bands and the fundamental frequencies $\text{ν}$_3′ of the excited ²A′ state could be determined; the values are $\text{ν}$_o(HO₂)=7028 ± 3 cm^?1, $\text{ν}$_o(DO₂)=7034 ± 8 cm^?, $\text{ν}$_3′(HO₂)=927 ± 10 cm^?, and $\text{ν}$_3′(DO₂)=940 ± 28 cm^?1.