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 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.

scholarly journals The Isotope Effect for Electromigration of Sodium Ions in Molten Sodium Nitrate

1972 ◽  
Vol 27 (2) ◽  
pp. 288-293
Author(s):  
Nobufusa Saito ◽  
Katsumi Hirano ◽  
Kohei Okuyama ◽  
Isao Okada
Keyword(s):  
Melting Point ◽  
Isotope Effect ◽  
Sodium Nitrate ◽  
Mass Effect ◽  
Relative Difference ◽  
Internal Mass ◽  
Sodium Ions ◽  
Molten Sodium

AbstractThe relative difference (Δb/b) between the internal electromigration mobilities of 22Na and 24Na in molten NaNO3 has been measured in the range 340 - 515 °C. The internal mass effect, μint= (Δb/b)/(Δm/m) is - 0.056 at 340 °C (melting point 308 °C), - 0.079 at 435 °C and - 0.068 at 515 °C. The errors in μint are ±0.002.

The photolysis of hexafluoroacetone

1956 ◽  
Vol 234 (1199) ◽  
pp. 476-488 ◽  
Keyword(s):  
Quantum Yield ◽  
Initial Step ◽  
Excited Molecule ◽  
Inert Gases ◽  
Wide Range ◽  
Electronically Excited ◽  
Photolytic Decomposition ◽  
Long Lifetime ◽  
The Stability ◽  
Excellent Source

The photolytic decomposition of hexafluoroacetone has been studied over a wide range of temperatures and pressures using light of wavelength 3130 Å. The initial step involves the production of CF 3 radicals, and the only products are C 2 F 6 and CO. The reaction is an excellent source of CF 3 radicals. The quantum yield diminishes with increasing pressure. A mechanism is suggested involving the participation of an electronically excited molecule of comparatively long lifetime, and the effect of various inert gases on the stability of this species is discussed.

scholarly journals The Temperature Dependence of the Isotope Effect for Electromigration of Potassium Ions in Molten Potassium Nitrate

1968 ◽  
Vol 23 (11) ◽  
pp. 1779-1782
Author(s):  
Arnold Lundén ◽  
Alf Ekhed
Keyword(s):  
Thermal Decomposition ◽  
Temperature Dependence ◽  
Isotope Effect ◽  
Separation Factor ◽  
Mass Effect ◽  
Potassium Nitrate ◽  
Relative Difference ◽  
Potassium Ions ◽  
Heavy Isotope ◽  
Significant Enrichment

The relative difference (Δb/b) between the electromigration mobilities of 39K and 41K in molten KNO3 has been measured over the range 354° to 586°C. The mass effect, μ= (Δb/b)/(Δm/m), becomes larger when the temperature is increased, following the relation—,u =0.0385+0.000124 (t-337)where t is the temperature in °C. Due to thermal decomposition, the nitrate is partly converted to nitrite, but it is proved by performing experiments with different initial concentrations of nitrite, that the isotope effect for potassium is not influenced noticeably by the concentration of the anions.The experiment is designed to give an enrichment of the heavy isotope 41K in a small anode compartment and in the upper part of the separation tube. However, it was possible to establish that a slight, but significant, enrichment of the light isotope 39K was obtained in the lower part of the separation tube, i. e. just above the opening into the large cathode compartment. A separation factor of 1.003 was estimated for this enrichment effect, which is due to non-ideal conditions of the experiment.

Nuclear Mass Dependence of the Dirac–Breit–Pauli Hamiltonian

1974 ◽  
Vol 52 (6) ◽  
pp. 536-540 ◽  
Author(s):  
Jacek Karwowski ◽  
Serafin Fraga
Keyword(s):  
Mass Effect ◽  
Mass Dependence ◽  
Neutral Atoms ◽  
Nuclear Mass ◽  
Specific Mass ◽  
Hartree Fock ◽  
Relativistic Mass ◽  
Mass Correction ◽  
Order Of Magnitude ◽  
Mass Dependent

The nuclear mass dependent (relativistic, specific, and normal) corrections for many electron atoms are discussed. Numerical values, determined from Hartree–Fock functions for all the neutral atoms from helium through nobelium, show that the relativistic mass correction, never included in actual calculations, is of the same order of magnitude as the specific mass effect.

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