The formation and detection of some low-lying excited electronic states of BrCl and other halogens M. A. A. A. By Clyne and J. Coxon Department of Chemistry, Queen Mary College, University of London, Mile End Road, London, E. 1 ( Communicated by J. W. Linnett, F.R.S.—Received 1 August 1968) [Plates 17 and 18] Forty-nine bands arising from 8 ^ v' ^ 2 and 14 ^ v" ^ 1 have been detected in the emission spectrum of BrCl(3iJ0+ -> x27+) from two sources: (i) the reaction of Br or Br2 with C102, in which BrCl(3I70+) is populated in the transfer reaction, Br + C102 -> BrCl + 02, (3) and (ii) the radiative combination of bromine and chlorine atoms, Br + Cl + (M) -> BrCl(3i70+) ( + jtf). (5) The populations of the higher levels of BrCl (3/70+) formed in reaction (3) are less than in reaction (5). In reaction (3), BrCl(3/Z0+) is evidently formed via a triangular transition state similar to that postulated previously; the rate constant, Jcz, was found to be (3*1 ± 0*3) x 1010 cm3 mole-1 s"1 at 300 °K.
Formation and detection of low-lying excited electronic states 425 bromine afterglow spectra excited by the radiative combination of a pair of halogen atoms (Bader & Ogryzlo 1964; Hutton & Wright 1965; Gibbs & Ogryzlo 1965).
426 M. A. A. Clyne and J. A. Coxon Although no attack by halogens on this lubricant occurred, some difficulty was encountered owing to the ease with which the halogens dissolve in fluorocarbon grease.
Formation and detection of low-lying excited electronic states 427 minimum at 440 ± 2 cm-1 was observed, clearly due to BrCl. On account of the presence of 37C1 and with approximately equal amounts of 79Br and 81Br, the position of the fundamental is not precisely defined. Using = 1*6 cm-1, we deduce that (i)"e = 443 + 2 cm-1 in good agreement with the previous work.
428 M. A. A. Clyne and J. A. Coxon We have found a lower limit at room temperatures for the rate constant of this reaction to be Jc1 > 1012 cm3 mole-1 s-1. This reaction is therefore more rapid at 300 °K than the related reaction of atomic oxygen with chlorine (Clyne & Coxon i966c) O + Cl2 -> CIO + Cl; A^298 = — 6*1 kcal.
Clyne & Coxon Proc. Roy. Soc. A, volume 298, plate 17 sure, mine 5mm oo0 pr- xb0 en = £ hweelit N,bete, s e: Ion sur g total pressurm from reacti2475, 2h expo mHctrur); mpede ms at 1-5 mission sm (1st or oEm at 5 orine r). ( = 0-2 with chlnd ordere, slit ation of bromine atoms posure, slit = 0-4mm (2essure: I-N, 2 h exposu0-425 mm (2nd order).
Clyne Coxon Proc. Roy. Soc. A, volume 298, plate 18 8 910111213 14 mm 475, 5 2 0-2 r); e = d e, slit 1st or r ( u s m o m p x 5 e 2 * h 0 , f = I-Ner). slit e: rd , ro h g total pressu0-35mm (1st I-N, argon: f 1*5 mmHe, slit = ressure order).
Formation and detection of low-lying excited electronic states 429 become diffuse and extended. On further decreasing the flow of bromine, a critical point was reached when the flame became unstable and moved rapidly downstream, often remaining in a metastable position at a bend or other region of perturbation in the flow system. The reaction of bromine with chlorine dioxide is therefore an unusual type of chain reaction, the kinetics of which will be discussed in a later section of this paper.
Formation and detection of low-lying excited electronic states 431 of figure 5 can be used to determine the absolute vibrational numbering of the ground state levels. There are strong reasons for assigning the two infrared progressions to v' = 2 and v' = 3, rather than to v' — 0 and 1 as suggested previously (Clyne & Coxon 1966a) (see later discussion). On this basis, the vibrational assignment shown in figure 2 and in the Deslandres table (table 5), was obtained.