A Multiconformational Transition State Theory Approach to OH Tropospheric Degradation of Fluorotelomer Aldehydes

Abstract

Experimental work on the OH‐initiated oxidation reactions of fluorotelomer aldehydes (FTALs) strongly suggests that the respective rate coefficients do not depend on the size of the CxF2x+1 fluoroalkyl chain. FTALs hence represent a challenging test to our multiconformer transition state theory (MC‐TST) protocol based on constrained transition state randomization (CTSR), since the calculated rate coefficients should not show significant variations with increasing values of . In this work we apply the MC‐TST/CTSR protocol to the cases and calculate both rate coefficients at 298.15 K with a value of cm3 molecule−1 s−1, practically coincident with the recommended experimental value of kexp= cm3 molecule−1 s−1. We also show that the use of tunneling corrections based on improved semiclassical TST is critical in obtaining Arrhenius‐Kooij curves with a correct behavior at lower temperatures.

Cost-effective approach for atmospheric accretion reactions: a case of peroxy radical addition to isoprene

“…The reaction rate coefficients were calculated with the multiconformational transition state theory (MC-TST) approach for the bimolecular reaction following the expression: 43–47 where the quantum-mechanical tunneling coefficient κ t is 1 for the reaction between heavy atoms, T is the room temperature (= 298.15 K), h is the Planck's constant, P ref is the reference pressure (= 2.45 × 10 19 molecules cm −3 ) and k B is the Boltzmann's constant. Q R, j and Q TS, i are the partition functions of the reactant (peroxy radical) and transition state conformers j and i , respectively, Q isop is a partition function for the isoprene conformer and Δ E j and Δ E i correspond to the zero-point corrected electronic energies of the reactant and transition state conformers relative to the lowest energy conformers, respectively.…”

“…The reaction rate coefficients were calculated with the multiconformational transition state theory (MC-TST) approach for the bimolecular reaction following the expression: [43][44][45][46][47]…”

Gas-Phase Oxidation of Atmospherically Relevant Unsaturated Hydrocarbons by Acyl Peroxy Radicals

“…The reaction rate coefficients were calculated using the multiconformer transition state theory (MC-TST) approach for bimolecular reaction following expression , k normalb normali = κ t k B T h P normalr normale normalf Q normalu normalh ∑ i a l l .25em T S .25em c o n f . exp ( − Δ E i k normalB T ) Q T S , i ∑ j a l l .25em normalR .25em c o n f . exp ( − Δ E j k normalB T ) Q normalR , j .25em exp ( − E normalT normalS − E normalR k normalB T ) …”

“…The reaction rate coefficients were calculated using the multiconformer transition state theory (MC-TST) approach for bimolecular reaction following expression , where κ t is the quantum-mechanical tunneling coefficient (κ t = 1 is used for the reaction between atoms other than hydrogen), T is the temperature (=298.15 K), h is the Planck’s constant, P ref is the reference pressure (=2.45 × 10 19 cm –3 ), and k B is the Boltzmann’s constant. Q R, j and Q TS, i are the partition functions of the reactant (peroxy radical) and transition state conformers, respectively, Q uh is a partition function for unsaturated hydrocarbons where only the lowest energy conformer was included in the partition function due to the large energy gap between that and the higher energy conformers.…”

“…All DFT calculations were conducted using Gaussian 16 RevC.02 software, 36 and single-point energies were calculated using ORCA version 5.0.3. 37,38 The reaction rate coefficients were calculated using the multiconformer transition state theory (MC-TST) approach for bimolecular reaction following expression 39,40 i k j j j j j y…”