X2Π Radical Research Articles

1+1′ resonant multiphoton ionisation of OH radicals via the A2Σ+ state: insights from direct comparison with A-X laser-induced fluorescence detection

A 1+1′ resonance-enhanced multiphoton ionisation (REMPI) scheme for OH X2Π radicals is characterised for a broad range of intermediate A2Σ+ (v = 1, J, Fi) levels. The intensities of OH A-X (1,0) transitions detected by subsequent fixed-frequency VUV ionisation are compared with those obtained by near simultaneous laser-induced fluorescence (LIF) measurements. The ratios of the 1+1′ REMPI to LIF signals are used to derive enhancement factors which reflect the VUV absorption to the OH A3Π, 3d, v = 0 Rydberg state and/or the fast autoionisation process that yields OH+ ions. The determination of the enhancement factors permits 1+1′ REMPI to be utilised as a quantitative state-specific probe of OH X2Π radicals.

The microwave spectrum of the OH X2Π radical in the ground and vibrationally-excited (ν ≤ 6) levels

The microwave absorption spectrum of the OH X2Π radical has been observed in all vibrational levels up to ν = 6. Experimental details are described of the tunable cavity and parallel plate Stark-modulated spectrometers employed for transitions below and above 23 GHz, respectively. The observed line frequencies, together with those reported by other workers, have been fitted using a non-linear least-squares routine with numerical diagonalization of the Hamiltonian matrix. Pseudo high-order corrections for centrifugal distortion of the Λ-doubling are required for the ν = 0 data, which now extend to J = 19/2 in the 2Π1/2 component. The various adjustable parameters of the Hamiltonian are compared with those of other similar models. The Λ-doubling and magnetic hyperfine constants for the different vibrational levels are reported, and several line frequencies of potential astrophysical significance are predicted.

Reaction kinetics involving ground X2Π and excited A2Σ+hydroxyl radicals. Part 1.—Quenching kinetics of OH A2Σ+and rate constants for reactions of OH X2Π with CH3CCl3and CO

Resonance fluorescence has been used to determine the rate constants k1 and k2(cm3 molecule–1 s–1)(1 σ) of elementary reactions of ground state OH X2Π radicals from 293 to 430 K: OH + CH3CCl3[graphic omitted]CH2CCl3+ H2O (1), log10k1=(–11.62 ± 0.14)–(1394 ± 113)/2.303 T; OH + CO [graphic omitted] CO2+ H (2), k2=(–12.66 ± 0.12)–(88 ± 40)/2.303 T.

Kinetic studies for diatomic free radicals using mass spectrometry. Part 3.—Elementary reactions involving BrO X2Π radicals

Elementary reactions involving BrO X2Π radicals have been studied at 298 K in a discharge-flow system linked to a mass spectrometer with collision-free sampling. Detection of BrO was made directly by means of the BrO+ ion current, calibrated in terms of absolute BrO concentrations using the rapid reaction (1), NO + BrO [graphic omitted] NO2+Br.(1) Rate constants at 298 K (cm3 molecule–1 s–1) are reported for the second order decay reaction (2), BrO + BrO [graphic omitted] 2 Br + O2(2) as well as for reaction (1): k1=(2.2 ± 0.4)× 10–11; k2=(6.4 ± 1.3)× 10–12 cm3 molecule s–1. In addition, the rate constant k3 for reaction of Br 2P3/2 atoms with O3(3), has been determined at 298 K: Br + O3 [graghic omitted] BrO + O2(3), k3=(1.2 ± 0.2)× 10–12 cm3 molecule–1 s–1.