Reactions of ¹S, ¹D, and ³P carbon atoms with water. Oxygen abstraction and intermolecular formaldehyde generation mechanisms; An MCSCF study

Abstract

Reactions of singlet and triplet carbon atoms with water are explored theoretically using CASSCF-MCQDPT2, CCSD, and DFT methodologies. The 1 S carbons are found to be unreactive. Depending on the carbon atom generation method and the reaction medium, gas-phase C( 3 P) attacking water may generate CO and atomic hydrogen as the end products. Reaction paths of the C( 1 D) þ H 2 O system are complicated due to the involvement of two reactive potential energy surfaces with branchings occurring along each. Modifications in product distributions for reactions taking place in condensed phases are elaborated. The decisive reaction conditions, under which the oxygen abstraction and intermolecular formaldehyde generation dominate, are suggested to clarify the discrepancy related with experimental CO observation. The findings are consistent with available experimental data on this system. Oxygen abstraction and intermolecular formaldehyde generation mechanisms suggested here are capable of serving as models for similar reactions of alcohols.

Irradiation of Water Ice by C+ Ions in the Cosmic Environment

“…What we do not observe, however, is the hydroxymethylene radical which features prominently in our previous work and in the work of others who have studied the interaction of C with water. [35][36][37] An intriguing aspect is that we do not observe the formation of CO 2 as in experiments involving amorphous solid water, although the dihydroxymethyl radical may be a precursor of CO 2 on a longer timescale. Another possibility is that the COH • reacts with an oxygen atom that has been produced by a higher energy projectile fully dissociating a water molecule, as observed in earlier work.…”

Adsorption Energies of Carbon, Nitrogen, and Oxygen Atoms on the Low-temperature Amorphous Water Ice: A Systematic Estimation from Quantum Chemistry Calculations

“…The formation of water-carbon adducts is also suggested for carbon atoms and water molecules in liquid helium droplets at ultra-lowtemperature (∼0.4 K, Krasnokutski & Huisken 2014). Previous quantum chemistry calculations support the observed reactivity of atomic carbon with water (Ahmed et al 1983;Ozkan & Dede 2012). Hickson et al (2016) argues the importance of tunneling effects on the enhancement of the C + H 2 O reaction at low temperature.…”

Quantum Tunneling Enhancement of the C + H2O and C + D2O Reactions at Low Temperature

“…There have been several previous calculations of the reaction of carbon atoms with water [16][17][18] for all stationary points were fully optimized at the aug-cc-pVQZ level for each method and frequencies were calculated for each method using a smaller basis set (aug-cc-pVTZ) at the CCSD(T) and MRCI+Q levels. For each TS, characterized by one imaginary frequency (first-order saddle points) on the PES, we determined the minimum energy pathways (MEPs) performing intrinsic reaction coordinate analyses (IRC) at the MP2 and DFT levels.…”

“…The C( 3 P 0,1,2 ) + H 2 O(X 1 A 1 ) reaction leads to 3 surfaces in the entrance valley, one with 3 Aʹ symmetry and two with 3 Aʹʹ symmetry when the C-atom approaches in C s geometry or 3 3 Aʹ 16 . CCSD(T) should lead to the most accurate values considering the T1 and D1 diagnostic values [47][48] in agreement with the fact that CASSCF calculations lead to monoconfigurational wavefunctions.…”

“…A schematic representation of the PES for the C-H 2 O system is shown in Fig. 1, based on current and previous [16][17] ab-initio calculations. Reaction occurs through C-atom addition to the O-atom of water forming a prereactive complex 30-40 kJ mol -1 lower than reagents.…”