Theoretical investigation of germane and germylene decomposition kinetics

Abstract

The dissociation kinetics of germane and its decomposition products were studied determining microcanonical kinetic constants with RRKM theory and integrating the master equation using a stochastic approach. Relevant reaction parameters were calculated through first principles calculations. Structures of reactants and transition states were determined at the B3LYP/aug-cc-pvtz level while energies were computed at the CCSD(T) level and extended to the complete basis set limit. Though similar for many aspects to the kinetics of decomposition of SiH(4), GeH(4) has some peculiar features that indicate a different chemical reactivity. It was found that the main decomposition channel leads to the formation of germylene, GeH(2), which rapidly decomposes to atomic Ge and H(2). The dissociation of GeH(2) to Ge and H(2) is a formally spin forbidden reaction characterized by an activation energy of 160.3 kJ mol(-1) calculated at the minimum energy crossing point between the singlet and triplet states. The intersystem crossing probability was explicitly included in the microcanonical simulations through Landau-Zener theory. It was found that its effect on the reaction rate is almost negligible, both because of the large spin-orbit coupling between the singlet and triplet states and for the fall off conditions prevailing in the examined pressure and temperature ranges. Kinetic constants of the main decomposition channels were determined as a function of pressure and temperature between 0.0013 and 10 bar and 1100 and 1700 K. The high and low pressure kinetic constants for GeH(4) decomposition are 6.4 x 10(13) (T/K)(0.272) exp(-26 700 K/T) and 2.7 x 10(48) (T/K)(-9.05) exp(-31 600 K/T), while those for GeH(2) are 6.02 x 10(12) (T/K)(0.203) exp(-19 660 K/T) and 1.6 x 10(26) (T/K)(-3.06) exp(-21 121 K/T), respectively. A quantitative agreement with experimental data for GeH(4) decomposition could be obtained adopting a downward energy transfer parameter of 340 x (T/298 K)(0.85) cm(-1) in the collisional model, and assuming that atomic Ge can react fast with GeH(4) to form Ge(2)H(2) and H(2), thus enhancing the germane decomposition rate and suggesting that a fast kinetic route leading to the Ge(2)H(2) production can be active in the gas phase.

Fulvenallene Decomposition Kinetics

“…TS* lies on the intrinsic reaction coordinate connecting W1 and W7 , so that, if the crossing between the singlet and triplet PES takes place, the reacting system evolves toward the minimum triplet energy well found in proximity of TS* , which is W18 . The possibility to compute the probability of intersystem crossing was recently included in our code by evaluating the k ( E , J ) microcanonical rate as suggested by Harvey: k ( E , J ) = ∫ 0 E − E 0 ρ ≠ false( E I , J false) p hop false( E − E 0 − E I false) d E I h normalρ ( E , J ) In this case, the microcanonical rate constant depends on p hop , the probability of intersystem hopping, which can be calculated from Landau–Zener theory as the probability of hopping in a double pass through the Minimum Energy Crossing Point (MECP) as p hop ( E ) = ( 1 − P LZ ) ( 1 + P LZ ) where the Landau–Zener transition probability was calculated as P LZ = exp ( − 2 normalπ…”

“…34 TS* lies on the intrinsic reaction coordinate connecting W1 and W7, so that, if the crossing between the singlet and triplet PES takes place, the reacting system evolves toward the minimum triplet energy well found in proximity of TS*, which is W18. The possibility to compute the probability of intersystem crossing was recently included in our code 59 by evaluating the k(E,J) microcanonical rate as suggested by Harvey: 60 kðE, JÞ ¼…”

Analysis of the Reactivity on the C7H6 Potential Energy Surface

“…Kinetic constants of decomposition reactions were determined using classic transition state theory except for dissociation into the fulvenallenyl radical and hydrogen, in which case microcanonical J -resolved variational transition state theory on RRKM K ( E , J ) rate constants was adopted, as described in our previous works. , In the evaluation of the kinetic constants, the possibility that low frequency vibrations could degenerate into hindered rotors was explicitly considered by investigating the rotational PES. When necessary (i.e., for relatively small rotational energetic barriers) the corresponding partition function was calculated using a hindered rotor model, with energy levels determined solving a one-dimensional Schrödinger equation as described in our previous works. , In calculating the kinetic constants, the reactant partition functions were assumed to be those of fulvenallene.…”

“…The kinetic constant of TS1 was calculated using microvariational J-resolved transition state theory as described by Polino The Journal of Physical Chemistry A ARTICLE et al, 63 using the CÀH PES sketched in Figure 1 and vibrational frequencies calculated along the reaction coordinate at the CASPT2/cc-pVTZ level. The analysis of the two lowest vibrational frequencies of TS30 has shown that they can be better treated as hindered rotations.…”

Toluene and benzyl decomposition mechanisms: elementary reactions and kinetic simulations

“…The reactivity on these PESs was studied by performing a comprehensive RRKM/master equation analysis with the stochastic kinetic Monte Carlo (KMC) code developed in our group. 38,46,47 The data used as input for the kinetic simulations are vibrational frequencies, rotational constants and relative energies of all the wells and transition states of the two reacting systems, calculated as described in the previous paragraph and reported in the ESI.w…”