Quantum dynamics of the photostability of pyrazine

2015 ◽  
Vol 17 (44) ◽  
pp. 29518-29530 ◽  
Author(s):  
Matthieu Sala ◽  
Stéphane Guérin ◽  
Fabien Gatti
Keyword(s):  
Electronic State ◽  
Ground State ◽  
Quantum Dynamics ◽  
Ground Electronic State ◽  
Conical Intersection ◽  
Radiationless Decay

We propose a new mechanism for the radiationless decay of photoexcited pyrazine to its ground electronic state involving a conical intersection between the dark Au(nπ) state and the ground state.

scholarly journals A deep UV trigger for ground-state ring-opening dynamics of 1,3-cyclohexadiene

2019 ◽  
Vol 5 (9) ◽  
pp. eaax6625 ◽  
Author(s):  
Jennifer M. Ruddock ◽  
Haiwang Yong ◽  
Brian Stankus ◽  
Wenpeng Du ◽  
Nathan Goff ◽  
...  
Keyword(s):  
Electronic State ◽  
Ground State ◽  
Ground Electronic State ◽  
Source Analysis ◽  
Time Resolved ◽  
X Ray Scattering ◽  
Linac Coherent Light Source ◽  
Scattering Anisotropy ◽  
Kinetics Of ◽  
Single Bonds

We explore the photo-induced kinetics of 1,3-cyclohexadiene upon excitation at 200 nm to the 3p state by ultrafast time-resolved, gas-phase x-ray scattering using the Linac Coherent Light Source. Analysis of the scattering anisotropy reveals that the excitation leads to the 3px and 3py Rydberg electronic states, which relax to the ground state with a time constant of 208 ± 11 fs. In contrast to the well-studied 266 nm excitation, at 200 nm the majority of the molecules (76 ± 3%) relax to vibrationally hot cyclohexadiene in the ground electronic state. A subsequent reaction on the ground electronic state surface leads from the hot cyclohexadiene to 1,3,5-hexatriene, with rates for the forward and backward reactions of 174 ± 13 and 355 ± 45 ps, respectively. The scattering pattern of the final hexatriene product reveals a thermal distribution of rotamers about the carbon-carbon single bonds.

scholarly journals Photodissociation of Iso-Propoxy (I-C3H7O) Radical at 248 Nm

2020 ◽  
Author(s):  
Erin Sullivan ◽  
Steven Saric ◽  
Daniel Neumark
Keyword(s):  
Electronic State ◽  
Ground State ◽  
Branching Ratio ◽  
Ground Electronic State ◽  
Angular Distributions ◽  
Translational Energy ◽  
Energy And Angular Distributions ◽  
Three Body ◽  
State Dissociation

<p>Photodissociation of the <i>i</i>-C<sub>3</sub>H<sub>7</sub>O radical is investigated using fast beam photofragment translational spectroscopy. Neutral <i>i</i>-C<sub>3</sub>H<sub>7</sub>O radicals are produced through the photodetachment of a fast beam of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O<sup>-</sup> anions and are subsequently dissociated using 248 nm (5.0 eV). The dominant product channels are CH<sub>3</sub> + CH<sub>3</sub>CHO and OH + C<sub>3</sub>H<sub>6</sub> with some contribution from H + C<sub>3</sub>H<sub>6</sub>O. CH<sub>3</sub> and H loss are attributed to dissociation on the ground electronic state of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O, but in a nonstatistical manner because RRKM dissociation rates exceed the rate of energy randomization. Translational energy and angular distributions for OH loss are consistent with ground state dissociation, but the branching ratio for this channel is considerably higher than predicted from RRKM rate calculations. These results corroborate what has been observed previously in C<sub>2</sub>H<sub>5</sub>O dissociation at 5.2 eV that yields CH<sub>3</sub>, H, and OH loss. Additionally, <i>i</i>-C<sub>3</sub>H<sub>7</sub>O undergoes three-body fragmentation to CH<sub>3</sub> + CH<sub>3</sub> + HCO and CH<sub>3</sub> + CH<sub>4</sub> + CO. These three-body channels are attributed to dissociation of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O to CH<sub>3</sub> + CH<sub>3</sub>CHO, followed by secondary dissociation of CH<sub>3</sub>CHO on its ground electronic state.</p>

scholarly journals Photodissociation of Iso-Propoxy (I-C3H7O) Radical at 248 Nm

2020 ◽  
Author(s):  
Erin Sullivan ◽  
Steven Saric ◽  
Daniel Neumark
Keyword(s):  
Electronic State ◽  
Ground State ◽  
Branching Ratio ◽  
Ground Electronic State ◽  
Angular Distributions ◽  
Translational Energy ◽  
Energy And Angular Distributions ◽  
Three Body ◽  
State Dissociation

<p>Photodissociation of the <i>i</i>-C<sub>3</sub>H<sub>7</sub>O radical is investigated using fast beam photofragment translational spectroscopy. Neutral <i>i</i>-C<sub>3</sub>H<sub>7</sub>O radicals are produced through the photodetachment of a fast beam of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O<sup>-</sup> anions and are subsequently dissociated using 248 nm (5.0 eV). The dominant product channels are CH<sub>3</sub> + CH<sub>3</sub>CHO and OH + C<sub>3</sub>H<sub>6</sub> with some contribution from H + C<sub>3</sub>H<sub>6</sub>O. CH<sub>3</sub> and H loss are attributed to dissociation on the ground electronic state of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O, but in a nonstatistical manner because RRKM dissociation rates exceed the rate of energy randomization. Translational energy and angular distributions for OH loss are consistent with ground state dissociation, but the branching ratio for this channel is considerably higher than predicted from RRKM rate calculations. These results corroborate what has been observed previously in C<sub>2</sub>H<sub>5</sub>O dissociation at 5.2 eV that yields CH<sub>3</sub>, H, and OH loss. Additionally, <i>i</i>-C<sub>3</sub>H<sub>7</sub>O undergoes three-body fragmentation to CH<sub>3</sub> + CH<sub>3</sub> + HCO and CH<sub>3</sub> + CH<sub>4</sub> + CO. These three-body channels are attributed to dissociation of <i>i</i>-C<sub>3</sub>H<sub>7</sub>O to CH<sub>3</sub> + CH<sub>3</sub>CHO, followed by secondary dissociation of CH<sub>3</sub>CHO on its ground electronic state.</p>

scholarly journals Time-Resolved Study of Light-Induced Ground State Proton Transfer from Acid Medium to 4-Nitrophenolate

2020 ◽  
Author(s):  
Leandro Scorsin ◽  
Leticia Martins ◽  
Haidi Fiedler ◽  
Faruk Nome ◽  
RENE NOME
Keyword(s):  
Acetic Acid ◽  
Proton Transfer ◽  
Electronic State ◽  
Ground State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Proton Transfer Reaction ◽  
Ground Electronic State ◽  
Experimental Conditions

In the present work, we study the transient laser-induced formation of 4-nitrophenolate (4-NPO<sup>-</sup>) in the ground electronic state and subsequent proton transfer reaction with acetic acid and water with numerical calculations and laser flash photolysis. We employ the Debye-Smoluchowski spherically-symmetric diffusion model of photoacid proton transfer to determine experimental conditions for studying thermally activated chemical reactions in the ground electronic state. Numerically calculated protonation and deprotonation probabilities for 4-NPO<sup>-</sup> and 4-nitrophenol (4-NPOH) in both ground and excited states showed the feasibility of efficiently producing the ground state anion in the photoacid cycle. We performed laser flash photolysis measurements of 4-NPOH to characterize the photo-initiated ground state protonation and deprotonation rate constants of 4-NPO<sup>-</sup>/4-NPOH as a function of acetic acid, pH, temperature and viscosity. Overall, the work presented here shows a simple way to study fast competing bimolecular proton transfer reactions in non-equilibrium conditions in the ground electronic state <i>(GSPT)</i>.

The ground state of KO revisited: the millimeter and submillimeter spectrum of potassium oxide

2019 ◽  
Vol 21 (39) ◽  
pp. 21960-21965 ◽  
Author(s):  
Mark A. Burton ◽  
Benjamin T. Russ ◽  
Matthew P. Bucchino ◽  
Phillip M. Sheridan ◽  
Lucy M. Ziurys
Keyword(s):  
Excited State ◽  
Electronic State ◽  
Millimeter Wave ◽  
Ground State ◽  
Wave Spectrum ◽  
Ground Electronic State ◽  
Potassium Oxide ◽  
Direct Absorption

Measurement of the millimeter-wave spectrum of the KO radical, using direct absorption methods, suggests that the ground electronic state is X2Πi with a close-lying excited state approximately 120 cm−1 higher in energy.

scholarly journals Time-Resolved Study of Light-Induced Ground State Proton Transfer from Acid Medium to 4-Nitrophenolate

2020 ◽  
Author(s):  
Leandro Scorsin ◽  
Leticia Martins ◽  
Haidi Fiedler ◽  
Faruk Nome ◽  
RENE NOME
Keyword(s):  
Acetic Acid ◽  
Proton Transfer ◽  
Electronic State ◽  
Ground State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Proton Transfer Reaction ◽  
Ground Electronic State ◽  
Experimental Conditions

In the present work, we study the transient laser-induced formation of 4-nitrophenolate (4-NPO<sup>-</sup>) in the ground electronic state and subsequent proton transfer reaction with acetic acid and water with numerical calculations and laser flash photolysis. We employ the Debye-Smoluchowski spherically-symmetric diffusion model of photoacid proton transfer to determine experimental conditions for studying thermally activated chemical reactions in the ground electronic state. Numerically calculated protonation and deprotonation probabilities for 4-NPO<sup>-</sup> and 4-nitrophenol (4-NPOH) in both ground and excited states showed the feasibility of efficiently producing the ground state anion in the photoacid cycle. We performed laser flash photolysis measurements of 4-NPOH to characterize the photo-initiated ground state protonation and deprotonation rate constants of 4-NPO<sup>-</sup>/4-NPOH as a function of acetic acid, pH, temperature and viscosity. Overall, the work presented here shows a simple way to study fast competing bimolecular proton transfer reactions in non-equilibrium conditions in the ground electronic state <i>(GSPT)</i>.

Photodissociation Dynamics of the Methylsulfinyl Radical at 248 nm

2018 ◽  
Author(s):  
Isaac Ramphal ◽  
Chin Lee ◽  
Daniel Neumark
Keyword(s):  
Excited State ◽  
Electronic State ◽  
Ground State ◽  
Molecular Beam ◽  
Internal Conversion ◽  
Ground Electronic State ◽  
Electronically Excited ◽  
State Dissociation ◽  
Primary Channel

The photodissociation dynamics of jet-cooled methylsulfinyl radicals, CH3SO, at 248 nm have been investigated using molecular beam photofragment translational spectroscopy. The primary channel is CH3S + O, which occurs via the initially prepared excited CH3SO state by rapid cleavage of the S-O bond to produce ground state products. The minor SO + CH3 channel has two components in comparable proportions: a fast feature corresponding to rapid C-S cleavage on the excited state to produce CH3 and electronically excited SO, and a slow feature due to internal conversion of CH3SO followed by statistical dissociation on the ground electronic state. Statistical ground state dissociation also produces small amounts of CH2SO, likely sulfine, and H-atoms.

Photodissociation Dynamics of the Methylsulfinyl Radical at 248 nm

2018 ◽  
Author(s):  
Isaac Ramphal ◽  
Chin Lee ◽  
Daniel Neumark
Keyword(s):  
Excited State ◽  
Electronic State ◽  
Ground State ◽  
Molecular Beam ◽  
Internal Conversion ◽  
Ground Electronic State ◽  
Electronically Excited ◽  
State Dissociation ◽  
Primary Channel

The photodissociation dynamics of jet-cooled methylsulfinyl radicals, CH3SO, at 248 nm have been investigated using molecular beam photofragment translational spectroscopy. The primary channel is CH3S + O, which occurs via the initially prepared excited CH3SO state by rapid cleavage of the S-O bond to produce ground state products. The minor SO + CH3 channel has two components in comparable proportions: a fast feature corresponding to rapid C-S cleavage on the excited state to produce CH3 and electronically excited SO, and a slow feature due to internal conversion of CH3SO followed by statistical dissociation on the ground electronic state. Statistical ground state dissociation also produces small amounts of CH2SO, likely sulfine, and H-atoms.

scholarly journals The Populations of H2 Vibrational States in Intense UV Fields Near O-B Stars

1987 ◽  
Vol 115 ◽  
pp. 179-180
Author(s):  
P. E. Dewdney ◽  
R. S. Roger ◽  
N. Robert
Keyword(s):  
Electronic State ◽  
Excited States ◽  
Ground State ◽  
Molecular Hydrogen ◽  
Ground Electronic State ◽  
Vibrational States ◽  
Vibrationally Excited ◽  
B Stars ◽  
Intense Fields ◽  
The Mean

In most places where molecular hydrogen exists in the interstellar medium, it will be found in the ground vibrational and ground electronic state. This will not be so, however, near 0 or early B stars where, in the region just beyond the ionization boundary, populations will be determined by UV fields up to 105 times more intense than the mean interstellar value (4 × 10−16 ergs cm−3 s−1 = 1 Habing unit). The H2 absorbs Lyman-Werner band photons longwards of λ91 nm and subsequent decays to the ground electronic state may lead to dissociation (vibrational continuum) or to one of 14 vibrationally excited states. Molecules in these states have lifetimes of order 1010 s and, in the intense fields, will be exposed to further Lyman-Werner excitation. The probability of dissociation is therefore greatly enhanced by this ‘multiple excitation’, since the number of lines available to vibrationally excited H2 is many times that available to ground-state H2 (Shull, 1978).

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