Unimolecular Reactions of E-Glycolaldehyde Oxide and Its Reactions with One and Two Water Molecules

The kinetics of Criegee intermediates are important for atmospheric modeling. However, the quantitative kinetics of Criegee intermediates are still very limited, especially for those with hydroxy groups. Here, we calculate rate constants for the unimolecular reaction of E-glycolaldehyde oxide [E-hydroxyethanal oxide, E-(CH2OH)CHOO], for its reactions with H2O and (H2O)2, and for the reaction of the E-(CH2OH)CHOO…H2O complex with H2O. For the highest level of electronic structure, we use W3X-L//CCSD(T)-F12a/cc-pVDZ-F12 for the unimolecular reaction and the reaction with water and W3X-L//DF-CCSD(T)-F12b/jun-cc-pVDZ for the reaction with 2 water molecules. For the dynamics, we use a dual-level strategy that combines conventional transition state theory with the highest level of electronic structure and multistructural canonical variational transition state theory with small-curvature tunneling with a validated density functional for the electronic structure. This dynamical treatment includes high-frequency anharmonicity, torsional anharmonicity, recrossing effects, and tunneling. We find that the unimolecular reaction of E-(CH2OH)CHOO depends on both temperature and pressure. The calculated results show that E-(CH2OH)CHOO…H2O + H2O is the dominant entrance channel, while previous investigations only considered Criegee intermediates + (H2O)2. In addition, we find that the atmospheric lifetime of E-(CH2OH)CHOO with respect to 2 water molecules is particularly short with a value of 1.71 × 10−6 s at 0 km, which is about 2 orders of magnitude shorter than those usually assumed for Criegee intermediate reactions with water dimer. We also find that the OH group in E-(CH2OH)CHOO enhances its reactivity.


Details of dual-level calculations of high-pressure-limit rate constants
The high-pressure-limit (HPL) bimolecular rate constants were calculated by the following dual-level expression: where '() is explained below, and are described in detail in Section 2 of the article, and +'+ = where R1 and R2 are the reactants, TS is the transition state, TST is conventional transition state theory, * , h, and are the Boltzmann constant, Planck constant, and temperature, respectively, Q is the partition function excluding translation, Φ ;<= is the relative translational partition function per unit volume, and + ,is the enthalpy of activation at 0 K, which equals the Born-Oppenheimer energy plus the zero-point vibrational energy.
Because we include zero-point vibrational energy in the exponential, the partition functions must be computed with their zero of energy at the zero-point level (although in most of our papers, we write partition functions with the zero of energy at the equilibrium structure or the saddle point, and we put potential energy without the zero-point vibrational energy in the exponential). The quantity ,-, --./0 results from a calculation employing the lowestenergy conformers of the reactants and transition states and using the higher-level electronic structure method, whereas ,-, --.00 denotes the same kind of calculation but at the lower level of electronic structure. The product '() is computed at the lower level of electronic structure.
For the isomerization, the treatment is the same except that 1# 12 Φ 345 is replaced by the partition function 1 of a single reactant.
For the calculation of isomerization of 1 and its reaction with water monomer, the higher level is Level 3, and for the calculation of [1 + H2O…H2O] and [C-1 + H2O], the higher level is Level 7.
&67 is the torsional anharmonicity factor for the reaction rate, and it is given by where 89 :9 denotes the effect of torsional anharmonicity on the transition state, and ; <-S-4 denotes the effect of torsional anharmonicity on the reactants (in the bimolecular case) or the reactant (in the unimolecular case). The quantities in eq 3 are calculated as the multistructure anharmonic partition function divided by the single-structure quasi-harmonic partition function.  Tables S19 and S20). Table A1. Electronic structure methods a Abbreviation Explanation Level-1 CCSD(T)-F12a/cc-pVDZ-F12 Level-2 DF-CCSD(T)-F12b/jun-cc-pVDZ a The levels defined here are the same as in Table 1 of the article proper, but the definitions of those involved in the SI are repeated here for convenience. S-7 where λ C = 0.997 for Level 1, and λ C = 0.995 for Level-2.  Table S6. Imaginary frequencies (in cm -1 ) of transition stats structures and mean unsigned  deviations from the best estimate   Method  TS-3a  TS-3b TS-3c  TS-3d  MUD   Level-2  457i  548i  509i  486i  0.00  M06CR/MG3S  484i  608i  561i  529i  45i  MN15-L/MG3S  577i  874i  770i  653i  218i  M11-L/MG3S  666i  980i  922i  708i  319i   Table S7. Enthalpies of activation at 0 K (in kcal/mol)) by using a reaction-specific scale factor (RSSF) from Table S2 or by using a generic scale factor (GSF) from :9 denotes the effect of torsional anharmonicity on a given reaction path. It was calculated by the lower-level electron structure method (M11-L/MG3S) with the generic scale factor. For this reaction path, five distinguishable conformers are included for reactants (see Figure S5), and five conformers are included for transition states (see Figure S6).  1.61 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method with a generic scale factor. For this reaction path, five distinguishable conformers are included for reactants (see Figure S5), and five conformers are included for transition state (see Figure S7).  3.15 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method with generic scale factors. For this reaction path, five distinguishable conformers are included for reactants (see Figure S5), and six conformers are included for transition state (see Figure S8).  4.00 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method with generic scale factors. For this reaction path, six distinguishable conformers are included for reactants (see Figure S9), and seven conformers are included for transition states (see Figure S10).  .97 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method with generic scale factors. For this reaction path, six distinguishable conformers are included for reactants (see Figure S9), and six conformers are included for transition states (see Figure S11).  .66 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method by using the generic scale factor. For this reaction path, six distinguishable conformers are included for reactants (see Figure S9), and six structures are included for transition states (see Figure S12).  1.04E-13 4.74E-14 5.57 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method by using the generic scale factor. For this reaction path, six distinguishable conformers are included for reactants (see Figure S9), and seven structures are included for transition states (see Figure S13).   Figure S5), and seven structures are included for transition states (see Figure S10).   Figure S5), and six conformers are included for transition states (see Figure S11).  1.62 9.40E-12 2.06E-12 8.65 a The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method by using the generic scale factor. For this reaction path, five distinguishable conformers are included for reactants (see Figure S5), and six conformers are included for transition states (see Figure S12).  The recrossing transmission coefficients, the tunneling transmission coefficients, and the torsional anharmonic factors were calculated by the lower-level electron structure method by using the generic scale factor. For this reaction path, five distinguishable conformers are included for reactants (see Figure S5), and seven conformers are included for transition states (see Figure S13).   ′ is the rate constants that goes through the tight transition state forming P2, and it comes from the sum of the four CAH IH in Tables S11-S14.     Table S19 and Table S20. S-25