Low-Temperature Kinetics of Reactions of the OH Radical with Propene and 1-Butene Studied by a Pulsed Laval Nozzle Apparatus Combined with Laser-Induced Fluorescence

Abstract

The kinetics of the reactions of the OH radical with propene and 1-butene are studied at T = 103 K. The low-temperature environment is provided by a pulsed Laval nozzle supersonic expansion of nitrogen with admixed radical precursor and reactant gases. The gas number density and temperature distributions in the flow are characterized by both dynamic pressure measurements and laser-induced fluorescence (LIF) spectroscopy of OH radicals excited in the (1,0) band of the A2Σ+−X2Πi transition. For the kinetic measurements, the OH radical decay profiles in the presence of reactants are monitored by LIF. The rate constants of the reactions of OH with propylene and 1-butene are measured at T = 103 K to be (0.81 ± 0.18) × 10-10 and (1.24 ± 0.27) × 10-10 cm3 molecule-1 s-1, respectively. The observed negative temperature dependences of the rate constants for both reactions studied by the pulsed Laval nozzle system show good agreement with both low-temperature and high-temperature kinetic data available in the literature.

Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures

“…The overall design is based on the pulsed version of a CRESU 165 apparatus pioneered by M. Smith and co-workers 24,28 , and subsequently adopted by the groups of Leone 22,23 and Abel. 25 The design is influenced by experience gained by the authors during the operation of continuous 6 and pulsed 23 Laval nozzle systems. A schematic of the overall experimental arrangement 170 of the apparatus is shown in Figure 1, consisting of a vacuum chamber and pumps, gas delivery system and reservoir, Laval nozzle, photolysis and probe laser systems, fluorescence collection system and data acquistion system.…”

“…At a density of 510 16 molecule cm -3 and 90 K it is expected that translational and rotational degrees of freedom are rapidly equilibrated, as has been observed in previous studies of such jets. 21,23,24 We have obtained the 595 rotational temperature by using LIF excitation spectra of either NO or OH to measure the rotational populations of several rotational levels and fitting a Boltzmann function to the data, or by a best fit to simulated spectra. The LIF signal excited from a ground-state with quantum number J, and 600 normalised for changes in laser power, is given by:…”

“…19, 20 130 The CRESU technique uses a continuous flow of gas and although able to produce temperatures down to 7 K 1 requires very large pumps and enormous flows of gases. A continuous system with a modest pumping capacity using short Laval nozzles has recently been developed and able to generate 135 temperaures as low as 77 K. 21 In order to reduce pumping capacity and gas flow considerably further, a number of pulsed CRESU systems have been developed, in which a short pulse of gas is expanded through the Laval nozzle, [22][23][24][25][26] achieving temperatures as low as 58 K, 25 and the reaction 140 initiated and monitored using LFP-LIF. In this paper we describe the pulsed Laval nozzle apparatus developed in Leeds and the results of experiments to characterise the spatial and temporal variation of temperature and density within the supersonic flow.…”

Reactions at Very Low Temperatures: Gas Kinetics at a New Frontier

“…The use of pulsed Laval nozzles has been pioneered by Smith and coworkers, [22] and the method has been adopted in a number of other laboratories. [23] Apparatuses incorporating pulsed Laval nozzles have time-averaged flows that are lower by factors of 10-100 than those employed in continuous-flow CRESU experiments. However, as yet, pulsed Laval nozzle experiments have not accessed the very low temperatures that have been reached in CRESU experiments, the lowest temperature reported being 58 K.…”

Kinetics in Cold Laval Nozzle Expansions: From Atmospheric Chemistry to Oxidation of Biomolecules in the Gas Phase

“…Recently, M. Smith's group at the University of Arizona (Tucson) in the US developed a pulsed Laval expansion apparatus that requires a much smaller pumping system. [11,12] Following up on this concept also Leone et al in Berkeley [13][14][15][16] and the Gçttingen group [17][18][19][20][21] have set up pulsed Laval nozzle machines and reported a couple of applications. This article presents some 'snapshots' of pulsed Laval nozzle technology applied for probing molecular dynamics at low temperatures, an overview of the application range of miniaturised pulsed Laval nozzles, as well as the new results that are generated with such a powerful approach.…”