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

Mausumi Ray; Biswajit Saha; George C. Schatz

doi:10.1021/jp3066629

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

Mausumi Ray, Biswajit Saha, George C. Schatz^*

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

6 Scopus citations

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 (a³Π_u) of the C₂ molecule is only 2.1 kcal/mol, two reactions, O(³P) + C ₂(X¹Σg₊) and O(³P) + C ₂(a³Π_u), 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(a³Π_u) 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(a³Π_u) 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(a³Π_u), about 50% of the available energy ends up as electronic excitation. The partitioning for each electronic state in the C₂(a³Π_u) 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 language	English (US)
Pages (from-to)	26577-26585
Number of pages	9
Journal	Journal of Physical Chemistry C
Volume	116
Issue number	50
DOIs	https://doi.org/10.1021/jp3066629
State	Published - Dec 20 2012

ASJC Scopus subject areas

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

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10.1021/jp3066629

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@article{affcdff2d1db4093a14d58da29c289b7,

title = "Theoretical studies of the O(3P) + C2 reaction at hyperthermal energies",

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.",

author = "Mausumi Ray and Biswajit Saha and Schatz, {George C.}",

year = "2012",

month = dec,

day = "20",

doi = "10.1021/jp3066629",

language = "English (US)",

volume = "116",

pages = "26577--26585",

journal = "Journal of Physical Chemistry C",

issn = "1932-7447",

publisher = "American Chemical Society",

number = "50",

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T1 - Theoretical studies of the O(3P) + C2 reaction at hyperthermal energies

AU - Ray, Mausumi

AU - Saha, Biswajit

AU - Schatz, George C.

PY - 2012/12/20

Y1 - 2012/12/20

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.

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

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