Thermochemical Properties of the Benzynes

2010 ◽  
Vol 63 (7) ◽  
pp. 1091 ◽  
Author(s):  
Paul G. Wenthold
Keyword(s):  
Excited State ◽  
Ground State ◽  
Thermochemical Data ◽  
Enthalpies Of Formation ◽  
Triplet States ◽  
Theoretical Studies ◽  
Thermochemical Properties ◽  
Starting Point ◽  
The Subject ◽  
The Absolute

The thermochemical properties of the benzynes have been the subject of investigation for nearly 50 years. This work provides an overview and assessment of all the experimental thermochemical properties that have been reported for the benzynes, or can be derived from reported thermochemical data. These properties include enthalpies of formation and thermochemical values that correspond to formation and dissociation of the benzynes by neutral and ionic processes. Thermochemical values are provided for both the ground-state singlet and the excited-state triplet states of the benzynes. The starting point for all the thermochemical consideration of the benzynes are the enthalpies of formation, which, in this work, are recommend to be 107.3 ± 3.5, 121.9 ± 3.1, and 138.0 ± 1.0 kcal mol–1 for ortho-, meta-, and para-benzyne, respectively (1 kcal mol–1 = 4.184 kJ mol–1). Whereas the paper predominantly focuses on the experimentally determined values, it also provides a comparison with theoretical studies that have examined the absolute thermochemical properties of the benzynes.

Monitoring the Formation and Decay of Transient Photosensitized Intermediates Using Pump-Probe UV Resonance Raman Spectroscopy. I: Self-Modeling Curve Resolution

2003 ◽  
Vol 57 (4) ◽  
pp. 439-447 ◽  
Author(s):  
James A. Kleimeyer ◽  
Joel M. Harris
Keyword(s):  
Factor Analysis ◽  
Excited State ◽  
Ground State ◽  
Pure Component ◽  
Triplet States ◽  
Time Resolved ◽  
Pump Probe ◽  
Excited Triplet ◽  
Curve Resolution ◽  
Excited Triplet States

Resolution of transient excited-state Raman scattering from ground-state and solvent bands is a challenging spectroscopic measurement since excited-state spectral features are often of low intensity, overlapping the dominant ground-state and solvent bands. The Raman spectra of these intermediates can be resolved, however, by acquiring time-resolved data and using multidimensional data analysis methods. In the absence of a physical model describing the kinetic behavior of a reaction, resolution of the pure-component spectra from these data can be accomplished using self-modeling curve resolution, a factor analysis technique that relies on the correlation in the data along a changing composition dimension to resolve the component spectra. A two-laser UV pump-probe resonance-enhanced Raman instrument was utilized to monitor the kinetics of amine quenching of excited-triplet states of benzophenone. The formation and decay of transient intermediates were monitored over time, from 15 ns to 100 μs. Factor analysis of the time-resolved spectral data identified three significant components in the data. The time-resolved intensities at each Raman wavenumber shift were projected onto the three significant eigenvectors, and least-squares criteria were developed to find the common plane in the space of the eigenvectors that includes the observed data. Within that plane, the three pure-component spectra were resolved using geometric criteria of convex hull analysis. The resolved spectra were found to arise from benzophenone excited-triplet states, diphenylketyl radicals, and the solvent and ground-state benzophenone.

Theoretical Studies on the Ground State and Excited State of 2,7-(Ethylene)-bis-8-hydroxyquinoline

2008 ◽  
Vol 21 (3) ◽  
pp. 263-269 ◽  
Author(s):  
Hui-xue Li ◽  
Su-juan Pan ◽  
Xiao-feng Wang ◽  
Tai Xiao
Keyword(s):  
Excited State ◽  
Ground State ◽  
Theoretical Studies

A new predissociated 2Σ+ state of the BeCl molecule

1977 ◽  
Vol 55 (6) ◽  
pp. 582-588 ◽  
Author(s):  
M. Carleer ◽  
B. Burtin ◽  
R. Colin
Keyword(s):  
Excited State ◽  
High Resolution ◽  
Dissociation Energy ◽  
Intensity Distribution ◽  
Internuclear Distance ◽  
Ground State ◽  
Thermochemical Data ◽  
Molecular Constants ◽  
Equilibrium Internuclear Distance ◽  
A Value

Ten bands belonging to a new B2Σ+–X2Σ+ system of the BeCl molecule have been discovered in emission between 1990 and 2175 Å. The bands of both isotopes Be35Cl and Be37Cl have been photographed at high resolution and the most intense ones have been rotationally analyzed. Only three levels of the excited state have been observed and they present vibrational and rotational perturbations. The principal molecular constants of the new B2Σ+ state of Be35Cl are: v00 = 48 827.6, ΔG1/2 = 925.5, ΔG3/2 = 1212.7, Be = 0.7751, De = 3.5 × 10−6 cm−1, and the equilibrium internuclear distance is 1.7422 Å. The unusual intensity distribution in the bands can be tentatively interpreted as the result of an inverse predissociation which leads to a value of D″0 = 27 800 ± 500 cm−1 (3.45 ± 0.06 eV) for the dissociation energy of the ground state of the BeCl molecule. This value is at variance with thermochemical data.

scholarly journals Low-Lying Electronic States of the Nickel Dimer

2021 ◽  
Vol 9 ◽  
Author(s):  
Patrick K. Tamukong ◽  
Mark R. Hoffmann
Keyword(s):  
Excited State ◽  
Ground State ◽  
Electronic States ◽  
Binding Energies ◽  
Spectroscopic Constants ◽  
Equilibrium Geometry ◽  
Dissociation Limit ◽  
Full Potential ◽  
Theoretical Studies ◽  
Dissociation Channel

The generalized Van Vleck second order multireference perturbation theory (GVVPT2) method was used to investigate the low-lying electronic states of Ni2. Because the nickel atom has an excitation energy of only 0.025 eV to its first excited state (the least in the first row of transition elements), Ni2 has a particularly large number of low-lying states. Full potential energy curves (PECs) of more than a dozen low-lying electronic states of Ni2, resulting from the atomic combinations 3F4 + 3F4 and 3D3 + 3D3, were computed. In agreement with previous theoretical studies, we found the lowest lying states of Ni2 to correlate with the 3D3 + 3D3 dissociation limit, and the holes in the d-subshells were in the subspace of delta orbitals (i.e., the so-dubbed δδ-states). In particular, the ground state was determined as X 1Γg and had spectroscopic constants: bond length (Re) = 2.26 Å, harmonic frequency (ωe) = 276.0 cm−1, and binding energy (De) = 1.75 eV; whereas the 1 1Σg+ excited state (with spectroscopic constants: Re = 2.26 Å, ωe = 276.8 cm−1, and De = 1.75) of the 3D3 + 3D3 dissociation channel lay at only 16.4 cm−1 (0.002 eV) above the ground state at the equilibrium geometry. Inclusion of scalar relativistic effects through the spin-free exact two component (sf-X2C) method reduced the bond lengths of both of these two states to 2.20 Å, and increased their binding energies to 1.95 eV and harmonic frequencies to 296.0 cm−1 for X 1Γg and 297.0 cm−1 for 1 1Σg+. These values are in good agreement with experimental values of Re = 2.1545 ± 0.0004 Å, ωe = 280 ± 20 cm−1, and D0 = 2.042 ± 0.002 eV for the ground state. All states considered within the 3F4 + 3F4 dissociation channel proved to be energetically high-lying and van der Waals-like in nature. In contrast to most previous theoretical studies of Ni2, full PECs of all considered electronic states of the molecule were produced.

scholarly journals Probing the excited state relaxation dynamics of pyrimidine nucleosides in chloroform solution

2016 ◽  
Vol 194 ◽  
pp. 683-708 ◽  
Author(s):  
Katharina Röttger ◽  
Hugo J. B. Marroux ◽  
Hendrik Böhnke ◽  
David T. J. Morris ◽  
Angus T. Voice ◽  
...  
Keyword(s):  
Excited State ◽  
Electronic State ◽  
Ground State ◽  
Experimental Studies ◽  
Chloroform Solution ◽  
Ground Electronic State ◽  
Triplet States ◽  
Relaxation Dynamics ◽  
State Recovery ◽  
Franck Condon

Ultrafast transient electronic and vibrational absorption spectroscopy (TEAS and TVAS) of 2′-deoxy-cytidine (dC) and 2′-deoxy-thymidine (dT) dissolved in chloroform examines their excited-state dynamics and the recovery of ground electronic state molecules following absorption of ultraviolet light. The chloroform serves as a weakly interacting solvent, allowing comparisons to be drawn with prior experimental studies of the photodynamics of these nucleosides in the gas phase and in polar solvents such as water. The pyrimidine base nucleosides have some propensity to dimerize in aprotic solvents, but the monomer photochemistry can be resolved clearly and is the focus of this study. UV absorption at a wavelength of 260 nm excites a 1ππ* ← S0 transition, but prompt crossing of a significant fraction (50% in dC, 17% in dT) of the 1ππ* population into a nearby 1nπ* state is too fast for the experiments to resolve. The remaining flux on the 1ππ* state leaves the vertical Franck–Condon region and encounters a conical intersection with the ground electronic state of ethylenic twist character. In dC, the 1ππ* state decays to the ground state with a time constant of 1.1 ± 0.1 ps. The lifetime of the 1nπ* state is much longer in the canonical forms of both molecules: recovery of the ground state population from these states occurs with time constants of 18.6 ± 1.1 ps in amino-oxo dC and ∼114 ps in dT, indicating potential energy barriers to the 1nπ*/S0 conical intersections. The small fraction of the imino-oxo tautomer of dC present in solution has a longer-lived 1nπ* state with a lifetime for ground state recovery of 193 ± 55 ps. No evidence is found for photo-induced tautomerization of amino-oxo dC to the imino-oxo form, or for population of low lying triplet states of this nucleoside. In contrast, ∼8% of the UV-excited dT molecules access the long-lived T1 (3ππ*) state through the 1nπ* state. The primary influence of the solvent appears to be the degree to which it destabilizes the states of 1nπ* character, with consequences for the lifetimes of these states as well as the triplet state yields.

Renilla Bioluminescence: A Morphologic Approach to the Location of Photocytes

1974 ◽  
Vol 32 ◽  
pp. 208-209
Author(s):  
Ben O. Spurlock ◽  
Milton J. Cormier
Keyword(s):  
Excited State ◽  
Ground State ◽  
Molecular Basis ◽  
Light Emission ◽  
Chemical Basis ◽  
Electronic Excited State ◽  
Colonial Form ◽  
The Common ◽  
Eighteenth And Nineteenth Centuries ◽  
Catalyzed Oxidation

The phenomenon of bioluminescence has fascinated layman and scientist alike for many centuries. During the eighteenth and nineteenth centuries a number of observations were reported on the physiology of bioluminescence in Renilla, the common sea pansy. More recently biochemists have directed their attention to the molecular basis of luminosity in this colonial form. These studies have centered primarily on defining the chemical basis for bioluminescence and its control. It is now established that bioluminescence in Renilla arises due to the luciferase-catalyzed oxidation of luciferin. This results in the creation of a product (oxyluciferin) in an electronic excited state. The transition of oxyluciferin from its excited state to the ground state leads to light emission.

Ground State and Excited State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor

1996 ◽  
Vol 6 (9) ◽  
pp. 1167-1180 ◽  
Author(s):  
A. Gicquel ◽  
M. Chenevier ◽  
Y. Breton ◽  
M. Petiau ◽  
J. P. Booth ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Microwave Plasma ◽  
Diamond Deposition

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

2020 ◽  
Author(s):  
Tomislav Rovis ◽  
Benjamin D. Ravetz ◽  
Nicholas E. S. Tay ◽  
Candice Joe ◽  
Melda Sezen-Edmonds ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Intersystem Crossing ◽  
Photoredox Catalysis ◽  
Infrared Irradiation ◽  
Triplet Excitation ◽  
New Family ◽  
Ir Light

We describe a new family of catalysts that undergo direct ground state singlet to excited state triplet excitation with IR light, leading to photoredox catalysis without the energy waste associated with intersystem crossing. The finding allows a mole scale reaction in batch using infrared irradiation.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

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