Discharge Flow-Photoionization Mass Spectrometric Study of HOI: Photoionization Efficiency Spectrum and Ionization Energy

Abstract

Photoionization efficiency (PIE) spectra of HOI were measured over the wavelength range A = 115-130 nm and in the ionization threshold region, A = 123-129 nm, using a discharge flow-photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. HOI was generated, in situ but in varying amounts, by three separate reactions: OH + I,; OH + CF3I; O(3P) + C2HJ The PIE spectra displayed steplike behavior near threshold, and the HO-I stretching frequency in the cation was determined to be 702 f 60 cm-I. A value of (9.811 & 0.020) eV was obtained for the adiabatic ionization energy (IE) of HOI from photoion thresholds, corresponding to the HOI+(X2A") -HOI(X' A') transition. Even though the present result appears to be the first reported determination of IE(HOI), the experimental value is compared to an estimated value previously derived via a trend analysis and it is considered in terms of trends in the series IE(HOX), where X = F, C1, Br, and I. The branching ratio for [HOI]/[IO] in the O(3P) + CzHJ reaction was estimated to be about 8/1 at T = 298 K if we assume that the photoionization efficiencies for HOI and IO are the same at 10.3 eV (A = 120 nm). Also, based on the value for IE(HO1) derived in the present study, a value for IE(I0) % 9.66 & 0.10 eV has been predicted.

298 K rate coefficients for the reaction of OH with <i>i</i> - C<sub>3</sub>H<sub>7</sub>I, <i>n</i> - C<sub>3</sub>H<sub>7</sub>I and C<sub>3</sub>H<sub>8</sub>

“…The products of the reaction of O( 3 P) with the iodo-propanes are IO, HOI, C 3 H 6 , and C 3 H 7 (Klaasen et al, 1996). By analogy with the reaction of O( 3 P + C 2 H 5 I (Monks et al, 1995) reaction (14a) is expected to dominate with a branching ratio close to 0.9.…”

Experimental and Computational Investigations of the Reaction of OH with CF3I and the Enthalpy of Formation of HOI

“…HOI is a major product of the reaction of ground-state atomic oxygen with C 2 H 5 I and larger iodoalkanes 4,5 and recently has been studied by photoionization 6 and FT-IR emission techniques. 7 ∆ f H 298 (HOI) has not previously been determined experimentally, despite its importance in understanding the photodissociation dynamics 8 and photoionization 6 of hypohalous acids and the roles of HOI in the mechanisms of iodine-mediated flame suppression 9 and stratospheric iodine chemistry. 10 Here we employ an ab initio potential energy surface (PES) to estimate the activation energy for the reverse rate constant k -1 and thus obtain the thermochemistry of reaction 1.…”

Photoionization Efficiency Spectrum and Ionization Energy of HSSH Produced from Gaseous Self-Reaction of HS Radicals

“…Thus, the threshold is not affected within the experimental uncertainty by thermal effects. [26][27][28] HS radicals were generated in the flow system via reaction 4a, which subsequently reacted with themselves to form HSSH. The reaction products were examined over the mass range m/z ) 30-90 at a photoionization wavelength of 110.0 nm (11.27 eV) after the flow system had been conditioned for at least 1 h. Reactant H 2 S was added into the flow system either from the injector or from the inlet port in the radical-generating region of the sidearm.…”