Development of the flowing afterglow/Langmuir probe technique for studying the neutral products of dissociative recombination using spectroscopic techniques: OH production in the HCO2+ + e reaction

DOI: 10.1063/1.457148

Source and publish data:

Journal of Chemical Physics p. 963 - 973 (1989)

Update date:2022-08-11

Topics:

Authors:

Adams, Nigel G.

Herd, Charles R.

Smith, David

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Article abstract of DOI:10.1063/1.457148

The flowing afterglow/Langmuir probe ( FALP ) technique has been extended to enable the neutral products of electron-ion dissociative recombination in thermalized afterglows to be identified by spectroscopic methods.Absolute number densities of H atoms in the afterglow have been determined using vacuum ultraviolet (VUV) absorption at the L_α wavelength.By exploiting the reaction H + NO2 -> OH + NO, all of the H atoms can be incorporated into OH molecules and thus observation of the intensity of laser induced fluorescence (LIF) I_f, obtained by exciting the (1,0) band of OH(A²Σ <- X²Π), allows a calibration to be obtained of I_f against the known number density of OH X²Π(ν = 0) in the afterglow.Following this procedure, a recombining HCO2⁺/electron afterglow was probed for production of ground state OHX²Π(ν = 0) using LIF and it was established that OH(ν = 0) resulted from 17percent of the recombining ground state HCO2⁺ ions.It was also established that a further 17percent of the recombinations resulted in OH(ν > 0), i.e., that, in total, (34 +/- 6)percent of the HCO2⁺ ions recombine to produce OH X²Π radicals, either directly or via the electronically excited A²Σ state.Details of the calibration procedure for H and OH number densities, of the ion chemistry involved in the production of the HCO2⁺ afterglow plasmas and of the checks carried out to establish that the fluorescence observed was from OH produced in the recombination reaction are presented.During these experiments, the rate coefficient at 300 K for the H + NO2 reaction was determined to be 1.3 X 10^-10 cm³ s^-1 from observations of the H-atom decay as a function of NO2 number density in the afterglow (in good agreement with previous determinations).Also the rate coefficient for the quenching reaction of OH(ν > 0) with NO to produce OH(v = 0) was determined to be 6 X 10^-11 cm³ s^-1.