Variation of the ion count rates for the association reactions of NH4+ with (a) (CH3)2O and (b) C2H5OH. The former plot illustrates the linearity that can be obtained in the primary ion decay (greater than two orders of magnitude) whilst in the latter, both the primary and secondary ions are illustrated showing the sequential clustering.

Whether reactions proceed, and the speed at which they occur, is central to chemistry. We study the kinetics of reactions between ions, electrons and neutral molecules in low pressure gas which are little influenced by solvent effects and thus reaction mechanisms can be investigated. As well as fundamental significance, the reactions are important in planetary atmospheres (including our environment), interstellar gas clouds where stars are forming, comets, combustion flames, plasmas used to etch semiconductor chips, etc. For these studies, we have developed flow tube apparatuses (selected ion flow tubes, SIFT, and flowing afterglows) coupled with a series of spectroscopic techniques (Vacuum Ultra-violet, visible, Infra-red emission and absorption spectroscopy, Laser Induced Fluorescence, etc.) covering the wavelength range 100 nm to 10 microns.

Recent successes have been (i) the identification of the isomeric forms of the products of reactions and the probing of the reaction potential energy surface (this is also a test of theory), (ii) the first determination of the products of the neutralization of a polyatomic ion, H₃O+, with electrons (H₃O+is everywhere that there is water and ionization). These studies are continuing with other molecular systems. Infra-red techniques are also being developed to observe rotationally resolved emissions from gas phase reactions to determine the product identities (elemental composition and isomeric form) and their electronic and vibrational states.

	download articles:		• Technique for distinguishing and determining the origin of photon emissions from complex plasmas • Selected ion flow tube study of NH4+ association and of product switching reactions with a series of organic molecules

SELECTED PUBLICATIONS

Williams, T.L., Adams, N.G., Babcock, L.M., Herd, C.R., Geoghegan, M. "Production and Loss of the Water Related Species H₃O+, H₂O and OH in Dense Interstellar Clouds," Mon. Not. Roy. Astron. Soc. 1996, 282, 413.

Matthews, K.K., Adams, N.G., Fisher, N.D. Isomeric Forms of the Products of the Collisional Associations of CH 3+with CH 3OH and H₃O+ with C₂H₄," J. Phys. Chem. 1997, 101, 2841.

Butler, J.M., Babcock, L.M., Adams, N.G. "Effects of Deuteration on Vibrational Excitation in the Products of the Electron Recombination of HCO+ and N₂H+," Molec. Phys. 1997, 91, 81.

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