Kinetics and dynamics of multi-channel unimolecular reactions of alkoxyl radicals over an extended range of temperature and pressure. A combined quantum chemical/RRKM dynamical study
Somnitz, H; Zellner, R
| HERO ID | 3407270 |
|---|---|
| In Press | No |
| Year | 2006 |
| Title | Kinetics and dynamics of multi-channel unimolecular reactions of alkoxyl radicals over an extended range of temperature and pressure. A combined quantum chemical/RRKM dynamical study |
| Authors | Somnitz, H; Zellner, R |
| Journal | Zeitschrift fur Physikalische Chemie |
| Volume | 220 |
| Issue | 8 |
| Page Numbers | 1029-1048 |
| Abstract | Rate coefficients and branching ratios for unimolecular reactions of alkoxyl radicals in the temperature range 200 to 1500 K and in the pressure range 10(-2) to 10(4) bar are presented. Special emphasis is given to the change of the relative importance of different reaction channels. This is evident for longer chain alkoxyl radicals which at lower temperatures undergo isomerisation via an energetically favourable six-member ring transition state. At temperatures above >600 K, however, the rates of the alternative decomposition pathways become faster than that of isomerisation. <br> <br>The theoretical approach to derive unimolecular rate coefficients makes use of extensive (G2/G3) ab initio calculations. These are used as input data for RRKM calculations to which a tunnelling probability of the generalised Eckart type has been included on the microcanonical level. A subsequent multi-channel master equation (ME) treatment yields thermal rate coefficients and complete fall-off curves for arbitrary pressure and temperature conditions. <br> <br>The kinetics of two linear chain alkoxyl radicals, 1-butoxyl and 2-pentoxyl, have been analysed to show the expected complex temperature and pressure behaviour resulting from the competition of multiple accessible reaction channels, each with its specific p, T-dependence. Additional results are reported for the minimum temperatures where channel switching can occur, the trajectory of these characteristic points on the p, T-surface, and the temperature dependence of the fractional ratios of the unimolecular reaction channels and the bimolecular reaction with oxygen at ambient atmospheric pressure. |
| Doi | 10.1524/zpch.2006.220.8.1029 |
| Wosid | WOS:000239944500003 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |
| Keyword | alkoxyl radicals; unimolecular reactions; RRKM-theory; tropospheric chemistry; combustion chemistry |