HOCO radical

Table 9.5 Vibrational frequencies (cm ) and IR intensities (km/mol) for HOCO radical...

The existence of the HOCO radical has been confirmed both in the gas-phase [85a] and in matrices [85b]. State-to-state integral cross sections for OH rotational excita-... 

Reaction (11), which may also proceed via collisional stabilisation to a HOCO radical has been the subject of numerous kinetic and dynamics studies over the past 30 years. At room temperature its rate constant is k29g = 1.5 x 10 cm molecule s but below 500 K the activation energy is almost zero. Recent measurements [11(b)] show that the rate constant only falls slightly as the temperature declines to 80 K. Unfortunately, the reaction is too slow to measure at lower temperatures in the present generation of CRESU experiments. The linear flow is so fast, that the first-order rate constant for decay of the radical concentration must be > 5 x 10 s with the result that any bimolecular reactions for which the rate constant is < 10 cm molecule s" cannot be successfully studied. 

Miyoshi, A., Matsui, H., Washida, N. Detection and reactions of the HOCO radical in gas phase. J. Chem. Phys. 100, 3532-3539 (1994)... 

Li, Q., M.C. Osborne, and l.W.M. Smith (2000a), Rate constants for the reactions of Cl atoms with HCOOH and with HOCO radicals, IrU. J. Chem. Kinet., 32, 85-91. 

When formic acid was codeposited at 14 K with a beam of excited argon atoms, formyl radical, HOCO, was produced (12) in sufficient yield for the IR detection of most of its vibrational fundamentals (Jacox, 1988). Detailed analysis of the matrix spectra of isotopically (D, C and 0) labelled formyl radical showed absorptions at 3603, 1844 and 1065cm , which correspond to the stretching vibrations of O—H, C=0 and C—O bonds. 

Normal coordinate analysis of the radical has been carried out and excellent agreement of experimental and calculated frequency values was obtained for the trans structure of HOCO. 

In (15), HOCO is the radical adduct of OH + CO, and HOCO is the adduct containing excess internal energy resulting from the energy released by bond formation between OH and CO. As described earlier, M is any molecule or atom that collides with the HOCO, removing some of its excess energy in practice, it is usually an inert bath gas such as He or Ar that is present in great excess over the reactants. 

An example of the application of transition state theory to atmospheric reactions is the reaction of OH with CO. As discussed earlier, this reaction is now believed to proceed by the formation of a radical adduct HOCO, which can decompose back to reactants or go on to form the products H + COz. For complex reactions such as this, transition state theory can be applied to the individual reaction steps, that is, to the steps shown in reaction (15). Figure 5.3 shows schematically the potential energy surface proposed for this reaction (Mozurkewich et al., 1984). The adduct HOCO, corresponding to a well on the potential energy surface, can either decompose back to reactants via the transition state shown as HOCO./ or form products via transition state HOCO,/. ... 

The p-halogenotetradecachlorotriphenylmethyl radicals. In the carbanion synthesis of the radical HOCO—PTM- from HOCO—PTM—H in the conventional manner, the radical I—PTM- is a minor by-product. It appears that the intermediate dianion OCO—PTM reacts rapidly with iodine, giving the radical OjC—PTM- (Ballester ct a/., 1982b Ibanez, 1972). High concentrations of iodine and/or long reaction times cause the formation of the radical I—PTM- as a major product by oxidative decarboxylation. It has been found that the dianion "O2C—PTM is stable under the reaction condition (Ballester et al., 1982b Ibanez, 1972). These results may be accounted for as shown in (142) through the intermediacy of acyclic,... 

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