The search for fluorescence and the study of radiationless transitions of electronic excited states of NH3+

1985 ◽  
Vol 63 (7) ◽  
pp. 1386-1389 ◽  
Author(s):  
Gérald Dujardin ◽  
Sydney Leach
Keyword(s):  
Quantum Yield ◽  
Potential Energy ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Dissociation Limit ◽  
Experimental Conditions ◽  
Electronic Excited States ◽  
Intramolecular Quenching ◽  
Upper Limits ◽  
Energy Surfaces

Photoion – fluorescence photon coincidence experiments were carried out in order to detect the fluorescence of NH3+ which is expected to occur from that part of its à electronic state that lies below the lowest dissociation limit. Hel and Nel sources were used to produce the ions. No NH3+ fluorescence was detected and upper limits for its quantum yield under our experimental conditions are given. We show that the lifetime of the à state is probably very long, making it difficult to observe fluorescence. Furthermore, we argue that the molecular parameters and potential energy surfaces of the à and [Formula: see text] states are such that resonance limit nonradiative coupling to high rovibrational levels of the [Formula: see text] state could be an efficient process for apparent intramolecular quenching of NH3+à state fluorescence.

Features of the thioformaldehyde potential energy surfaces

1985 ◽  
Vol 63 (7) ◽  
pp. 1910-1917 ◽  
Author(s):  
John D. Goddard
Keyword(s):  
Potential Energy ◽  
Excited States ◽  
Configuration Interaction ◽  
Potential Energy Surfaces ◽  
Transition States ◽  
Basis Sets ◽  
Dissociation Limit ◽  
Molecular Dissociation ◽  
Energy Surfaces ◽  
Higher Excited States

The structures of seven minima and five transition states of the S0 and T1 potential energy surfaces of thioformaldehyde have been located at the 3-21G* SCF level. Further calculations have been carried out to determine harmonic vibrational frequencies and to examine the effects of larger basis sets and of configuration interaction on energy differences. The molecular dissociation limit of H2 and CS is thermodynamically accessible at the energy of the lowest n,π* excited states and the singlet thiohydroxymethylenes lie only slightly too high. However, there are large barriers of ~85 to 90 kcal mol−1 to the molecular dissociation or to the 1,2-hydrogen shifts from thioformaldehyde to the thiohydroxymethylenes. The dissociation to H and HCS requires ~85.4 kcal mol−1 on the ground singlet and faces a barrier of several kcal mol−1 relative to products on the triplet surface. Any unimolecular photochemistry of thioformaldehyde is likely to require excitation to higher excited states than the lowest n,π* states.

Excited State Tracking During the Relaxation of Coordination Compounds

2018 ◽  
Author(s):  
Juan Sanz García ◽  
Martial Boggio-Pasqua ◽  
Ilaria Ciofini ◽  
Marco Campetella
Keyword(s):  
Excited State ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Photochemical Reactions ◽  
Complex Nature ◽  
Electronic Excited States ◽  
Ruthenium Nitrosyl ◽  
State Tracking ◽  
Energy Surfaces ◽  
Electronic Wavefunction

<div>The ability to locate minima on electronic excited states (ESs) potential energy surfaces (PESs) both in the case of bright and dark states is crucial for a full understanding of photochemical reactions. This task has become a standard practice for small- to medium-sized organic chromophores thanks to the constant developments in the field of computational photochemistry. However, this remains a very challenging effort when it comes to the optimization of ESs of transition metal complexes (TMCs), not only due to the presence of several electronic excited states close in energy, but also due to the complex nature of the excited states involved. In this article, we present a simple yet powerful method to follow an excited state of interest during a structural optimization in the case of TMC, based on the use of a compact hole-particle representation of the electronic transition, namely the natural transition orbitals (NTOs). State tracking using NTOs is unambiguously accomplished by computing the mono-electronic wavefunction overlap between consecutive steps of the optimization. Here, we demonstrate that this simple but robust procedure works not only in the case of the cytosine but also in the case of the ES optimization of a ruthenium-nitrosyl complex which is very problematic with standard approaches.</div>

scholarly journals Beyond the Coulson–Fischer point: characterizing single excitation CI and TDDFT for excited states in single bond dissociations

2019 ◽  
Vol 21 (39) ◽  
pp. 21761-21775 ◽  
Author(s):  
Diptarka Hait ◽  
Adam Rettig ◽  
Martin Head-Gordon
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Excited States ◽  
Potential Energy Surfaces ◽  
Single Bond ◽  
State Potential ◽  
Energy Surfaces ◽  
Single Bonds

HF/DFT orbitals spin-polarize when single bonds are stretched past the Coulson–Fischer point. We report unphysical features in the excited state potential energy surfaces predicted by CIS/TDDFT in this regime, and characterize their origin.

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