The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes

1985 ◽  
Vol 63 (7) ◽  
pp. 1424-1430 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers
Keyword(s):  
Ground State ◽  
Internal Conversion ◽  
Rydberg State ◽  
Singlet State ◽  
Hydrogen Shift ◽  
Geometric Isomerization ◽  
Trans Isomerization ◽  
Show Evidence ◽  
Structural Isomerization ◽  
Π State

We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes. Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization. This kind of isomerization increases with an increase in the number of alkyl substituents around the double bond. These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1π,π* state is involved in the cis–trans isomerization process; (b) the 1π,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state. Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.

The use of localized and delocalized orbitals in a Rydberg expanded correlation analysis of the cycloaddition of ethylene

1983 ◽  
Vol 61 (2) ◽  
pp. 306-311 ◽  
Author(s):  
Earl M. Evleth ◽  
Emil Kassab
Keyword(s):  
Correlation Analysis ◽  
Ground State ◽  
Rydberg State ◽  
Singlet State ◽  
Correlation Diagram ◽  
State Correlation ◽  
Localized State ◽  
Valence Level

Rydberg expanded orbital and state correlation diagrams are shown for the classical cycloaddition of ethylene. The diagrams are first developed at the localized valence MO level and the origins of the S**-bitriplet correlations are shown. When extended to the Rydberg level, the localized state correlation diagram shows that the π3s Rydberg singlet state of ethylene can interact with the ground state of another ethylene to directly yield the same S** surface as found in the valence-level-only diagram. In this manner the Rydberg state eventually derydbergizes.

The solution-phase photochemistry of 2-trifluoromethylnorbornene

1990 ◽  
Vol 68 (11) ◽  
pp. 1961-1966 ◽  
Author(s):  
N. Nguyen ◽  
B. E. Harris ◽  
K. B. Clark ◽  
W. J. Leigh
Keyword(s):  
Rydberg State ◽  
Singlet State ◽  
High Energy ◽  
Sigmatropic Rearrangement ◽  
Solution Phase ◽  
Excited Singlet ◽  
Direct Photolysis ◽  
Additional Support ◽  
193 Nm ◽  
Π State

The photochemistry of 2-trifluoromethylnorbornene in pentane solution has been investigated. Direct photolysis with 193 nm light yields 1-trifluoromethyl-2-norcarene in 90% yield, due to formal [1,3]-sigmatropic rearrangement, in addition to three other minor products. Chlorobenzene-sensitized photolysis affords photoreduction products, principally exo- and endo-2-trifluoromethylnorbornane and decane isomers, in addition to several products of higher molecular weight. On the basis of comparisons of the photochemistry of this compound to that previously reported for norbornene and 2-cyanonorbornene, as well as spectroscopic evidence, it is suggested that the lowest excited singlet state (the photoreactive state in solution) in 2-trifluoromethylnorbornene is the π, π* state. The results indicate that trifluoromethyl substitution has the effect of significantly raising the energy of the π,R(3s) Rydberg state in simple alkenes, without altering the high energy (ca. 6.5 eV) or the localized character of the alkene π, π* state. Furthermore, they lend additional support to the view that the carbene-derived products typically formed upon photolysis of alkenes in solution are derived from π,R(3s) excitation. Keywords: Rydberg, photolysis, far-uv, alkene, solution phase, singlet, triplet.

scholarly journals Photodissociation Dynamics of the Cyclohexyl Radical from the 3p Rydberg State at 248 nm

2021 ◽  
Author(s):  
Isaac Ramphal ◽  
Mark Shapero ◽  
Daniel Neumark
Keyword(s):  
Ground State ◽  
Ring Opening ◽  
Internal Conversion ◽  
Rydberg State ◽  
Laser Light ◽  
Slow Component ◽  
Translational Energy ◽  
Alkyl Radicals ◽  
Atom Loss ◽  
Similar Yield

The photodissociation of jet-cooled cyclohexyl was studied by exciting the radicals to their 3p Rydberg state using 248 nm laser light and detecting photoproducts by photofragment translational spectroscopy. Both H-atom loss and dissociation to heavy fragment pairs are observed. The H-atom loss channel exhibits a two-component translational energy distribution. The fast photoproduct component is attributed to impulsive cleavage directly from an excited state, likely the Rydberg 3s state, forming cyclohexene. The slow component is due to statistical decomposition of hot cyclohexyl radicals that internally convert to the ground electronic state prior to H-atom loss. The fast and slow components are present in a ~0.7:1 ratio, similar to findings in other alkyl radicals. Internal conversion to the ground state also leads to ring-opening followed by dissociation to 1-buten-4-yl + ethene in comparable yield to H-loss, with the C<sub>4</sub>H<sub>7</sub> fragment containing enough internal energy to dissociate further to butadiene via H-atom loss. A very minor ground-state C<sub>5</sub>H<sub>8</sub> + CH<sub>3</sub> channel is observed, attributed predominantly to 1,3-pentadiene formation. The ground-state branching ratios agree well with RRKM calculations, which also predict C<sub>4</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>5</sub> and C<sub>3</sub>H<sub>6</sub> + C<sub>3</sub>H<sub>5</sub> channels with similar yield to C<sub>5</sub>H<sub>8</sub> + CH<sub>3</sub>. If these channels were active it was at levels too low to be observed.

scholarly journals Photodissociation Dynamics of the Cyclohexyl Radical from the 3p Rydberg State at 248 nm

2021 ◽  
Author(s):  
Isaac Ramphal ◽  
Mark Shapero ◽  
Daniel Neumark
Keyword(s):  
Ground State ◽  
Ring Opening ◽  
Internal Conversion ◽  
Rydberg State ◽  
Laser Light ◽  
Slow Component ◽  
Translational Energy ◽  
Alkyl Radicals ◽  
Atom Loss ◽  
Similar Yield

The photodissociation of jet-cooled cyclohexyl was studied by exciting the radicals to their 3p Rydberg state using 248 nm laser light and detecting photoproducts by photofragment translational spectroscopy. Both H-atom loss and dissociation to heavy fragment pairs are observed. The H-atom loss channel exhibits a two-component translational energy distribution. The fast photoproduct component is attributed to impulsive cleavage directly from an excited state, likely the Rydberg 3s state, forming cyclohexene. The slow component is due to statistical decomposition of hot cyclohexyl radicals that internally convert to the ground electronic state prior to H-atom loss. The fast and slow components are present in a ~0.7:1 ratio, similar to findings in other alkyl radicals. Internal conversion to the ground state also leads to ring-opening followed by dissociation to 1-buten-4-yl + ethene in comparable yield to H-loss, with the C<sub>4</sub>H<sub>7</sub> fragment containing enough internal energy to dissociate further to butadiene via H-atom loss. A very minor ground-state C<sub>5</sub>H<sub>8</sub> + CH<sub>3</sub> channel is observed, attributed predominantly to 1,3-pentadiene formation. The ground-state branching ratios agree well with RRKM calculations, which also predict C<sub>4</sub>H<sub>6</sub> + C<sub>2</sub>H<sub>5</sub> and C<sub>3</sub>H<sub>6</sub> + C<sub>3</sub>H<sub>5</sub> channels with similar yield to C<sub>5</sub>H<sub>8</sub> + CH<sub>3</sub>. If these channels were active it was at levels too low to be observed.

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>

ROTATIONAL ANALYSIS OF THE β BANDS OF PHOSPHORUS MONOXIDE

1959 ◽  
Vol 37 (2) ◽  
pp. 136-143 ◽  
Author(s):  
Nand Lal Singh
Keyword(s):  
Ground State ◽  
Band System ◽  
Electronic States ◽  
Rotational Analysis ◽  
Rotational Constants ◽  
Fine Structures ◽  
Π State

The fine structures of three of the β bands of PO which occur near 3200 Å have been analyzed. The analysis shows that the upper state of this band system is a 2Σ and not a 2Π state as previously believed. The rotational constants of both electronic states have been determined and it is found that the ground state constants, previously determined from the γ bands, are incorrect.

Rotational Analysis of the lΠ–XlΣ+ System of C80Se

1974 ◽  
Vol 52 (9) ◽  
pp. 813-820 ◽  
Author(s):  
René Stringat ◽  
Jean-Paul Bacci ◽  
Marie-Hélène Pischedda
Keyword(s):  
Emission Spectrum ◽  
Ground State ◽  
High Frequency ◽  
Rotational Analysis ◽  
Molecular Constants ◽  
High Frequency Discharge ◽  
Perturbed State ◽  
Simple Evaluation ◽  
Π State

The strongly perturbed 1Π–X1Σ+ system of C80Se has been observed in the emission spectrum of a high frequency discharge through selenium and carbon traces in a neon atmosphere. The analysis of five bands yields, for the molecular constants of the ground state, the values Be″ = 0.5750 cm−1, [Formula: see text], αe″ = 0.00379 cm−1, re″ = 1.676 Å, ΔG″(1/2) = 1025.64 cm−1, and ΔG″(3/2) = 1015.92 cm−1. The numerous perturbations in the 1Π state prohibit the simple evaluation of the constants of the perturbed state and of the perturbing ones.

Photophysics of trioxatriangulenium ion. Electrophilic reactivity in the ground state and excited singlet state

2002 ◽  
Vol 1 (10) ◽  
pp. 763-773 ◽  
Author(s):  
Jóhannes Reynisson ◽  
Robert Wilbrandt ◽  
Vibeke Brinck ◽  
Bo W. Laursen ◽  
Kasper Nørgaard ◽  
...  
Keyword(s):  
Ground State ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Electrophilic Reactivity
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