Excited-Atom Production by Electron Bombardment of Alkali-Halides

1986 ◽  
Vol 75 ◽  
Author(s):  
R. E. Walkup ◽  
Ph. Avouris ◽  
A. P. Ghosh
Keyword(s):  
Gas Phase ◽  
Excited States ◽  
Ground State ◽  
Excited Atom ◽  
Alkali Halides ◽  
Electron Bombardment ◽  
Secondary Electrons ◽  
Excited Atoms ◽  
Positive Ions ◽  
Electronically Excited

AbstractWe present experimental results which suggest a new mechanism for the production of excited atoms and ions by electron bombardment of alkali-halides. Doppler shift measurements show that the electronically excited atoms have a thermal velocity distribution in equilibrium with the surface temperature. Measurements of the absolute yield of excited atoms, the distribution of population among the excited states, and the dependence of yield on incident electron current support a model in which excited atoms are produced by gas-phase collisions between desorbed ground-state atoms and secondary electrons. Similarly, gas-phase ionization of ground-state neutrals by secondary electrons accounts for a substantial portion of the positive ions produced by electron bombardment of alkali-halides.

Determination of Ionization Efficiencies of Excited Atoms in a Flame by Laser-Enhanced Ionization Spectrometry

1989 ◽  
Vol 43 (6) ◽  
pp. 940-952 ◽  
Author(s):  
O. Axner ◽  
T. Berglind
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Energy Difference ◽  
Ionization Efficiency ◽  
Striking Feature ◽  
Boltzmann Factor ◽  
Excited Atoms ◽  
Ionization Limit

State-specific ionization efficiencies for excited Li and Na atoms in acetylene/air flames have been determined. The ionization efficiencies, i.e., the probability that the excited atoms ionize instead of returning to the ground state, are determined by relating collision-assisted Laser-Enhanced Ionization (LEI) signals from various excited states with laser-induced photoionization signals. The ionization efficiencies are found to decrease (from being one at the ionization limit) almost monotonically as the lower atoms are excited. The most striking feature, however, is that the decrease of the ionization efficiency values is generally found to be less than the decrease of the Boltzmann factor, exp(- δE/kT), when the energy difference, δE, between the excited state and the ionization limit is increased. The ionization efficiencies are found to be close to unity for states with δE < kT and approximately 50% for states with δE ≈ 2.5 kT ( np ≈ 6 p). For the lower states, the ionization efficiencies are found to be approximately five times larger than the Boltzmann factor.

scholarly journals Photochemistry of Thymine in Protic Polar Nanomeric Droplets Using Electrostatic Embeding TD-DFT/MM

Molecules ◽  
2021 ◽  
Vol 26 (19) ◽  
pp. 6021
Author(s):  
Miquel Huix-Rotllant
Keyword(s):  
Gas Phase ◽  
Excited States ◽  
Ground State ◽  
Potential Energy Surfaces ◽  
Radiative Decay ◽  
Td Dft ◽  
Dna Photodamage ◽  
Solvent Molecules ◽  
Energy Surfaces ◽  
Electrostatic Embedding

Thymine photochemistry is important for understanding DNA photodamage. In the gas phase, thymine undergoes a fast non-radiative decay from S2 to S1. In the S1 state, it gets trapped for several picoseconds until returning to the ground-state S0. Here, we explore the electrostatic effects of nanomeric droplets of methanol and water on the excited states of thymine. For this purpose, we develop and implement an electrostatic embedding TD-DFT/MM method based on a QM/MM coupling defined through electrostatic potential fitting charges. We show that both in methanol and water, the mechanism is similar to the gas phase. The solvent molecules participate in defining the branching plane of S0/S1 intersection and have a negligible effect on the S1/S2 intersection. Despite the wrong topology of the ground/excited state intersections, electrostatic embedding TD-DFT/MM allows for a fast exploration of the potential energy surfaces and a qualitative picture of the photophysics of thymine in solvent droplets.

The structure and vertical excitation energies of the chlorothioformyl radical, ClCS: implications for the photofragmentation of thiophosgene

1993 ◽  
Vol 71 (1) ◽  
pp. 112-117 ◽  
Author(s):  
M. Hachey ◽  
F. Grein ◽  
R. P. Steer
Keyword(s):  
Energy Level ◽  
Ab Initio ◽  
Excited States ◽  
Ground State ◽  
Excited Electronic State ◽  
Excitation Energies ◽  
Electronically Excited States ◽  
Vertical Excitation ◽  
Electronically Excited ◽  
Vertical Excitation Energies

Ab initio CI studies have been performed to determine the geometry of the ground and first electronically excited states of the chlorothioformyl radical, ClCS, and the vertical excitation energies of its ten lowest doublet states and two lowest quartet states. The results are used to construct a more complete energy level correlation diagram for the photofragmentation of Cl2CS. The lowest excited electronic state of ClCS lies only 0.79 eV (adiabatic) above the ground state. Its discovery indicates that the results of previous photofragmentation experiments may need to be reinterpreted.

Comparative Study of the Photostability of Two Glycine Molecules in Different Medium

MRS Advances ◽  
2019 ◽  
Vol 4 (28-29) ◽  
pp. 1631-1637
Author(s):  
Satish Kumar ◽  
Ashok Jangid
Keyword(s):  
Excited States ◽  
Ground State ◽  
Minimum Energy ◽  
Quantum Mechanical ◽  
Minimum Energy Path ◽  
Electronically Excited States ◽  
Derivative Coupling ◽  
Mechanical Methods ◽  
Electronically Excited ◽  
Homo And Lumo

ABSTRACTThe photostability of two glycine molecules has been investigated using quantum mechanical methods i.e. at CASSCF/NEVPT2 level theory. It is found that the molecule in water shows vast photostability as a comparison to vacuum. The energies are calculated around HOMO and LUMO orbital. The NEVPT2 computed energies are reasonably matched with experimental results. The study shows that the molecule returns from higher electronically excited states to ground state through CI and AC crossings and these crossings provide a minimum energy path along derivative coupling and gradient differences vector.

Dynamics of the KrF* Laser Multiphoton Dissociation of a Series of Arene Chromium Tricarbonyls

1988 ◽  
Vol 131 ◽  
Author(s):  
George W. Tyndall ◽  
Robert L. Jackson
Keyword(s):  
Gas Phase ◽  
Excited States ◽  
Dissociation Process ◽  
Parent Molecule ◽  
Electronically Excited ◽  
Arene Ligand ◽  
Multiphoton Dissociation ◽  
Sequential Absorption ◽  
The One ◽  
Direct Dissociation

ABSTRACTThe KrF* (248 nim) laser multiphoton dissociation (MPD) of a series of (arene)chromium tricarbonyls has been investigated in the gas-phase using emission spectroscopy to detect the excited state photoproducts. In the MPD of all compounds studied, chromium atoms are formed in a variety of electronically excited states via a two-channel dissociation mechanism. The predominant pathway for formation of the ground electronic state and the lowest excited states is by a sequential absorption/fragmentation process, where the product of the one-photon dissociation of the parent molecule absorbs an additional photon and dissociates to Cr(I). The higher energy Cr(I) states are formed exclusively by a direct dissociation process, where the parent absorbs multiple photons prior to dissociation. The distribution of excited chromium atoms formed in the direct channel is statistical for all compounds studied and is independent of the nature of the arene ligand. In contrast, the distribution of Cr(I) states formed via the sequential dissociation channel is strongly dependent on the vibrational density of states in the arene ligand.

Electronic Structure of the Transition Elements

1973 ◽  
Vol 51 (6) ◽  
pp. 644-647
Author(s):  
K. M. S. Saxena ◽  
S. Fraga
Keyword(s):  
Electronic Structure ◽  
Excited States ◽  
Ground State ◽  
Ground States ◽  
Negative Ions ◽  
State Function ◽  
Transition Elements ◽  
Hartree Fock ◽  
Positive Ions ◽  
Single Set

Numerical Hartree–Fock functions have been determined for the ground states and first excited states of the configurations 3dN4s0 and 3dN4s2 for the negative ions, neutral atoms, and first four positive ions of all the transition elements. The validity of the approximation, embodied in the use of a single set of parameters determined from the ground state function of a configuration for the prediction of the spectroscopic levels arising from it, has been examined in detail in the case of Fe I, 3d64s2, where independent calculations have been carried out for all the excited states.

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