THE FAILURE OF CS APPROXIMATION IN QUANTUM REACTION SCATTERING WITH DOUBLE DEEP WELL: TIME-DEPENDENT CALCULATION FOR O + NH REACTION

Abstract

The present paper shows the failure of CS (centrifugal sudden or coupled states) approximation in the time-dependent (TD) quantum wave packet calculation for the exoergicity reaction O + NH on the 1A potential energy surface [Guadagnini, Schatz and Walch, J Chem Phys 102:774 (1995)] that has double deep wells. In order to show this, total reaction probabilities and rate constants for the title reaction are presented in this study with the CS approximation and the CC (close-coupling) method, respectively. The results show that by carrying out the wave packet propagation to several picoseconds with the CC method, we can resolve all the resonance features for the title reaction and the differences between the CS and the CC become larger as J becomes larger. When J becomes larger the agreement between the CS and the CC gets progressively worse. The failure of the CS approximation can be explained with the results of double deep wells, which cause long propagation time and make the coupling of K states important.

Progress and Prospective of Nitrogen-Based Alternative Fuels

“…While reviewing prior data on this reaction, Dean and Bozzelli calculated the coefficient of eq using the aforementioned DHT approach, with the resulting room-temperature value below the Hack et al upper limit. Wang et al applied the TDWP method with both CC and CS approximations to calculate the overall reaction rate coefficient, finding that the CS approximation severely undervalues the reaction’s temperature dependence . When Baulch et al reviewed this reaction they fitted a new coefficient for eq that approximates both the low-temperature measurements of Adamson et al and the high-temperature measurements of Mertens et al Finally, Li et al used the QM and (MRCI + Q) methods with AVQZ basis set to calculate the rate coefficients of both reaction channels at 298 K, with an overall coefficient value close to several previous room-temperature measurements …”

“…453 While reviewing prior data on this reaction, Dean and Bozzelli calculated the coefficient of eq 63 using the aforementioned DHT approach, 309 with the resulting roomtemperature value below the 455 To compare the above data, three separate figures were created, describing the total rate coefficient (Figure 32a) and the rate coefficient of eq 56 (Figure 32b) and eq 63 (Figure 32c). In several cases, 448,453,454 data were extracted from the literature and fitted to the modified Arrhenius form, for which the parameters are presented in Table S16. As can be seen in Figure 32a, several of the aforementioned early NH + O rate coefficient estimates are not in agreement with later calculations and measurements.…”