ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A procedure to calculate the quantum mechanical transition probability of a unimolecular primary chemical process, A- → A + e- is investigated for the circumstance where A- and A have different numbers of vibrational and rotational degrees of freedom (one is linear, the other not). A procedure is introduced to deal with the coupling between the vibrational and rotational motions. The proposed method was applied to calculating the lifetimes of CO2·- and N2O·- in the gas phase. The geometry optimizations and frequency calculations for CO2, CO2·-, N2O, and N2O·- are performed at HF, MP2, and QCISD(T) levels with 6-31G* or 6-31+G* basis sets, in order to obtain reliable geometric and spectroscopic information on these systems. Lifetimes are calculated for several of the lower vibrational-rotational states of the anions, as well as for the Boltzmann distribution of states at 298 K. The lifetime of the lowest vibrational-rotational state of CO2·-, is 1.03 × 10-4 s, and of the lowest vibrational state with rotational levels weighted by Boltzmann distribution at 298 K, 1.50 × 10-4 s. These values are in good agreement with the experimental number, 9.0 ± 2.0 × 10-5 s, and support the experimental evidence that CO2·- was formed in its ground vibrational level by the techniques used. The lifetime of CO2·- calculated with Boltzmann distribution over its vibrational and rotational levels at 298 K, is 1.51 × 10-5 s. There are no direct measurements of the lifetime of N2O·-, but it was estimated to be greater than 10-4 s from experimental evidence. The predicted lifetimes of N2O·-, at its lowest vibrational-rotational state (0 K) and lowest vibrational state with rotational levels weighted by the Boltzmann distribution at 298 K, are 238 and 19.1 s, respectively. The lifetime of N2O·- at thermal equilibrium at 298 K is 6.66 × 10-2 s, indicating that electron loss from the excited vibrational states of N2O·- is significant. This study represents the first theoretical investigation of CO2·- and N2O·- lifetimes. © 1994 John Wiley & Sons, Inc.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550260104
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