A non‐mass‐dependent isotope effect in the production of ozone from molecular oxygen

1983 ◽  
Vol 78 (2) ◽  
pp. 892-895 ◽  
Author(s):  
John E. Heidenreich ◽  
Mark H. Thiemens
Keyword(s):  
Molecular Oxygen ◽  
Isotope Effect ◽  
Mass Dependent

ISOTOPE EFFECT IN SURFACE PHOTOCHEMICAL PROCESSES: EXPERIMENT AND THEORY

1992 ◽  
Vol 06 (30) ◽  
pp. 1893-1910 ◽  
Author(s):  
X.-Y. ZHU
Keyword(s):  
Isotope Effect ◽  
Excited Molecule ◽  
Mass Effect ◽  
Photochemical Process ◽  
Quenching Process ◽  
Electronically Excited ◽  
Recent Variation ◽  
Mass Dependent ◽  
Chemical Event ◽  
Insight Into

A photochemical process in the adsorbate state has an inherent isotope or mass effect. This is because the presence of a solid surface introduces efficient relaxation channels for the electronically excited molecule. Competition between the chemical event and the quenching process is mass-dependent. Depending on the details of the dynamic energy transfer process, the isotope effect in a surface photochemical event can depend on either the mass or the internal reduced mass of the desorbing/dissociating particle. Measurements of isotope effect in UV surface photochemistry have provided insight into two mechanistic models, i.e., the classic Menzel-Gomer-Redhead (MGR) model and its recent variation, the vibration-mediated UV photodesorption (VMPD) model.

scholarly journals Multiple-sulfur isotope effects during photolysis of carbonyl sulfide

2011 ◽  
Vol 11 (19) ◽  
pp. 10283-10292 ◽  
Author(s):  
Y. Lin ◽  
M. S. Sim ◽  
S. Ono
Keyword(s):  
Isotope Effect ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Carbonyl Sulfide ◽  
State Theory ◽  
Abstraction Reaction ◽  
Isotope Ratio Mass Spectrometer ◽  
Ultraviolet Photolysis ◽  
Mass Dependent ◽  
Mass Dependent Fractionation

Abstract. Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S0). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N2 bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S0 and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF6 as the analyte gas. The isotope fractionation after correction for the reservoir effects is −6.8‰ for the ratio 34S/32S, where product S0 is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N2 but increases to −9.5‰ when radiation of λ > 285 nm is used. The measured isotope effect reflects that of photolysis as well as the subsequent sulfur abstraction (from OCS) reaction. The magnitude of isotope effects for the abstraction reaction is estimated by transition state theory to be between −18.9 and −3.1‰ for 34S which gives the photolysis isotope effect as −10.5 to +5.3‰. The observed triple isotope coefficients are ln(δ34S + 1)/ln(δ34S + 1) = 0.534 ± 0.005 and ln(δ36S + 1)/ln(δ34S + 1) = 1.980 ± 0.021. These values differ from canonical values for mass-dependent fractionation of 0.515 and 1.90, respectively. The result demonstrates that the OCS photolysis does not produce large isotope effects of more than about 10‰ for 34S/32S, and can be the major source of background stratospheric sulfate aerosol (SSA) during volcanic quiescence.

scholarly journals Time-dependent view of an isotope effect in electron-nuclear nonequilibrium dynamics with applications to N2

2018 ◽  
Vol 115 (23) ◽  
pp. 5890-5895 ◽  
Author(s):  
Jayanth S. Ajay ◽  
Ksenia G. Komarova ◽  
Francoise Remacle ◽  
R. D. Levine
Keyword(s):  
Isotope Effect ◽  
Wave Packets ◽  
Large Population ◽  
Isotopic Fractionation ◽  
Electronic States ◽  
Excited Molecule ◽  
Time Dependent ◽  
Nonequilibrium Dynamics ◽  
Effective Transfer ◽  
Mass Dependent

Isotopic fractionation in the photodissociation of N2 could explain the considerable variation in the 14N/15N ratio in different regions of our galaxy. We previously proposed that such an isotope effect is due to coupling of photoexcited bound valence and Rydberg electronic states in the frequency range where there is strong state mixing. We here identify features of the role of the mass in the dynamics through a time-dependent quantum-mechanical simulation. The photoexcitation of N2 is by an ultrashort pulse so that the process has a sharply defined origin in time and so that we can monitor the isolated molecule dynamics in time. An ultrafast pulse is necessarily broad in frequency and spans several excited electronic states. Each excited molecule is therefore not in a given electronic state but in a superposition state. A short time after excitation, there is a fairly sharp onset of a mass-dependent large population transfer when wave packets on two different electronic states in the same molecule overlap. This coherent overlap of the wave packets on different electronic states in the region of strong coupling allows an effective transfer of population that is very mass dependent. The extent of the transfer depends on the product of the populations on the two different electronic states and on their relative phase. It is as if two molecules collide but the process occurs within one molecule, a molecule that is simultaneously in both states. An analytical toy model recovers the (strong) mass and energy dependence.

Kinetic Isotope Effect in the Gas-Phase Reaction of Muonium with Molecular Oxygen

1999 ◽  
Vol 103 (13) ◽  
pp. 2076-2087 ◽  
Author(s):  
Ulrich Himmer ◽  
Herbert Dilger ◽  
Emil Roduner ◽  
James J. Pan ◽  
Donald J. Arseneau ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Oxygen ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Kinetic Isotope

scholarly journals Multiple-sulfur isotope effects during photolysis of carbonyl sulfide

2011 ◽  
Vol 11 (5) ◽  
pp. 14233-14258 ◽  
Author(s):  
Y. Lin ◽  
M. S. Sim ◽  
S. Ono
Keyword(s):  
Isotope Effect ◽  
Sulfur Isotope ◽  
Isotope Effects ◽  
Carbonyl Sulfide ◽  
State Theory ◽  
Abstraction Reaction ◽  
Isotope Ratio Mass Spectrometer ◽  
Ultraviolet Photolysis ◽  
Mass Dependent ◽  
Mass Dependent Fractionation

Abstract. Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S0). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N2 bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S0 and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF6 as the analyte gas. The isotope effect after correction for the reservoir effects is −6.8 ‰ for the ratio 34S/32S, where product S0 is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N2 but increases to −9.5 ‰ when radiation of λ >285 nm is used. The measured isotope effect reflects that of photolysis as well as the subsequent sulfur abstraction (from OCS) reaction. The magnitude of isotope effects for the abstraction reaction is estimated by transition state theory to be between −18.9 and −3.1 ‰ for 34S which gives the photolysis isotope effect as −10.5 to +5.3 ‰. The measured isotope effects are found to be δ33S/δ34S = 0.534±0.005 and δ36S/δ34S = 1.980±0.021. These values are largely mass-dependent but statistically differ from canonical values for mass-dependent fractionation of 0.515 and 1.90, respectively. The result demonstrates that the OCS photolysis may not produce large isotope effect of more than about 10 \\permil, and can be the major source of background stratospheric sulfate aerosol (SSA) during volcanic quiescence.

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