Theoretical studies of the O(3P) + C2 reaction at hyperthermal energies

Mausumi Ray, Biswajit Saha, George C Schatz

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Abstract

The O + C2 reaction has been investigated with the quasiclassical trajectory (QCT) method in conjunction with direct dynamics electronic structure calculations using density functional theory (DFT) forces. Trajectory surface-hopping calculations have also been performed to study spin-forbidden reactions. Calculations were performed at collision energies of 1-5 eV so as to simulate conditions relevant to erosion of carbon-based materials on spacecraft in low Earth orbit (LEO). Since the energy difference between the electronic ground state (X1Σg+) and the first excited triplet state (a3Πu) of the C2 molecule is only 2.1 kcal/mol, two reactions, O(3P) + C 2(X1Σg+) and O(3P) + C 2(a3Πu), have been studied. We present here the detailed mechanism, electronic branching, product energy disposal, and angular distribution for these reactions. The calculations show that the O( 3P) + C2(a3Πu) reaction can occur on singlet, triplet, and quintet surfaces to give the spin-allowed electronically excited CO(1Σ) + C(1D), CO( 3Π) + C(3P), and CO(3Π) + C( 1D) products as well as the ground state product CO( 1Σ) + C(3P), with CO(3Π) + C( 3P) being the most important, while O(3P) + C 2(X1Σg+) reacts on triplet surfaces to give primarily the CO(1Σ) + C(3P) product with only minor branching to spin-forbidden excited states. Reactions at 1 eV energy proceed on all surfaces through formation of the collision complex CCO, while the collision complex only forms briefly at 5 eV. The CO + C cross section for O(3P) reacting with C2(a3Πu) is three times smaller than with C2(X1Σg+). Angular distributions show that the product CO + C is more and more backward scattered as collision energy is increased as can be explained in terms of collision lifetime shortening at higher energies. Product energy disposal shows that for O(3P) + C2(X1Σg+) about 50% of the total available energy is deposited in relative translation, 10% is in CO rotation, and 40% is in CO vibration. For O(3P) + C 2(a3Πu), about 50% of the available energy ends up as electronic excitation. The partitioning for each electronic state in the C2(a3Πu) reaction is strongly state dependent, but for CO(3Π) + C(3P) product vibrational excitation accounts for 60% of the energy in excess of electronic energy.

Original languageEnglish
Pages (from-to)26577-26585
Number of pages9
JournalJournal of Physical Chemistry C
Volume116
Issue number50
DOIs
Publication statusPublished - Dec 20 2012

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Carbon Monoxide
Angular distribution
Excited states
Ground state
Trajectories
products
energy
collisions
Electronic states
Electronic structure
Density functional theory
electronics
Spacecraft
Erosion
disposal
Orbits
Earth (planet)
Molecules
Carbon
angular distribution

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Theoretical studies of the O(3P) + C2 reaction at hyperthermal energies. / Ray, Mausumi; Saha, Biswajit; Schatz, George C.

In: Journal of Physical Chemistry C, Vol. 116, No. 50, 20.12.2012, p. 26577-26585.

Research output: Contribution to journalArticle

Ray, Mausumi ; Saha, Biswajit ; Schatz, George C. / Theoretical studies of the O(3P) + C2 reaction at hyperthermal energies. In: Journal of Physical Chemistry C. 2012 ; Vol. 116, No. 50. pp. 26577-26585.
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abstract = "The O + C2 reaction has been investigated with the quasiclassical trajectory (QCT) method in conjunction with direct dynamics electronic structure calculations using density functional theory (DFT) forces. Trajectory surface-hopping calculations have also been performed to study spin-forbidden reactions. Calculations were performed at collision energies of 1-5 eV so as to simulate conditions relevant to erosion of carbon-based materials on spacecraft in low Earth orbit (LEO). Since the energy difference between the electronic ground state (X1Σg+) and the first excited triplet state (a3Πu) of the C2 molecule is only 2.1 kcal/mol, two reactions, O(3P) + C 2(X1Σg+) and O(3P) + C 2(a3Πu), have been studied. We present here the detailed mechanism, electronic branching, product energy disposal, and angular distribution for these reactions. The calculations show that the O( 3P) + C2(a3Πu) reaction can occur on singlet, triplet, and quintet surfaces to give the spin-allowed electronically excited CO(1Σ) + C(1D), CO( 3Π) + C(3P), and CO(3Π) + C( 1D) products as well as the ground state product CO( 1Σ) + C(3P), with CO(3Π) + C( 3P) being the most important, while O(3P) + C 2(X1Σg+) reacts on triplet surfaces to give primarily the CO(1Σ) + C(3P) product with only minor branching to spin-forbidden excited states. Reactions at 1 eV energy proceed on all surfaces through formation of the collision complex CCO, while the collision complex only forms briefly at 5 eV. The CO + C cross section for O(3P) reacting with C2(a3Πu) is three times smaller than with C2(X1Σg+). Angular distributions show that the product CO + C is more and more backward scattered as collision energy is increased as can be explained in terms of collision lifetime shortening at higher energies. Product energy disposal shows that for O(3P) + C2(X1Σg+) about 50{\%} of the total available energy is deposited in relative translation, 10{\%} is in CO rotation, and 40{\%} is in CO vibration. For O(3P) + C 2(a3Πu), about 50{\%} of the available energy ends up as electronic excitation. The partitioning for each electronic state in the C2(a3Πu) reaction is strongly state dependent, but for CO(3Π) + C(3P) product vibrational excitation accounts for 60{\%} of the energy in excess of electronic energy.",
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N2 - The O + C2 reaction has been investigated with the quasiclassical trajectory (QCT) method in conjunction with direct dynamics electronic structure calculations using density functional theory (DFT) forces. Trajectory surface-hopping calculations have also been performed to study spin-forbidden reactions. Calculations were performed at collision energies of 1-5 eV so as to simulate conditions relevant to erosion of carbon-based materials on spacecraft in low Earth orbit (LEO). Since the energy difference between the electronic ground state (X1Σg+) and the first excited triplet state (a3Πu) of the C2 molecule is only 2.1 kcal/mol, two reactions, O(3P) + C 2(X1Σg+) and O(3P) + C 2(a3Πu), have been studied. We present here the detailed mechanism, electronic branching, product energy disposal, and angular distribution for these reactions. The calculations show that the O( 3P) + C2(a3Πu) reaction can occur on singlet, triplet, and quintet surfaces to give the spin-allowed electronically excited CO(1Σ) + C(1D), CO( 3Π) + C(3P), and CO(3Π) + C( 1D) products as well as the ground state product CO( 1Σ) + C(3P), with CO(3Π) + C( 3P) being the most important, while O(3P) + C 2(X1Σg+) reacts on triplet surfaces to give primarily the CO(1Σ) + C(3P) product with only minor branching to spin-forbidden excited states. Reactions at 1 eV energy proceed on all surfaces through formation of the collision complex CCO, while the collision complex only forms briefly at 5 eV. The CO + C cross section for O(3P) reacting with C2(a3Πu) is three times smaller than with C2(X1Σg+). Angular distributions show that the product CO + C is more and more backward scattered as collision energy is increased as can be explained in terms of collision lifetime shortening at higher energies. Product energy disposal shows that for O(3P) + C2(X1Σg+) about 50% of the total available energy is deposited in relative translation, 10% is in CO rotation, and 40% is in CO vibration. For O(3P) + C 2(a3Πu), about 50% of the available energy ends up as electronic excitation. The partitioning for each electronic state in the C2(a3Πu) reaction is strongly state dependent, but for CO(3Π) + C(3P) product vibrational excitation accounts for 60% of the energy in excess of electronic energy.

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