ChemRate program

ChemRate program of Tsang and coworkers [102], and the VariFlex program [103] provide more general kinetics programs which include conventional RRKM theory with Eckart or other simple one-dimensional tunneling corrections. 

The rate constant for the association reaction channel (7c) was calculated in the temperature range from 200 to 2500 K and the pressure range from 1x10 to 7.6x10 Torr with the Variflex code [35], whereas those for channels (7b) and (7c) were computed with the ChemRate program... 

Programs such as Variflex [39], CHARMMRATE [40], or ChemRate [30] have the capability to calculate rate constants for reactions with no barrier, though both contain adjustable parameters and appear to work best if the rate constants can be anchored to experimental data. 

Other molecular parameters are obtained from CBS-QB3 ab initio calculations. Since the ab initio data do not yield the observed -factor, we adjusted the reaction path degeneracy in those applications that calculate the TST rates directly from molecular data (ChemRate, Unimol). Programs such as CARRA and MultiWell accept high-pressure rate constants in Arrhenius form as input and no adjustments were needed in these cases. The programs CARRA MSC and CARRA ME calculate the density of states from three characteristic frequencies instead of taking the complete set of frequencies, which we obtained with a separate fitting program. 

Fig. 6b contains results from ChemRate calculations with various values. The relation between this parameter and the predictions is obvious a larger unimolecular dissociation rate at low pressures and in the fall-off region. A consequence of this observation is that for each program an optimal [Pg.160]

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