Ultrafast Dynamics of 1,3-Cyclohexadiene in Highly Excited States

Buhler, Christine C.; Minitti, Michael P.; Deb, Sanghamitra; Bao, Jie J.; Weber, Peter M.

doi:10.1155/2011/637593

Cited by 13 publications

(23 citation statements)

References 27 publications

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“…The time constant in the low energy region of the spectrum can be related to the depopulation time of the excited state. Moreover, the spectra of CPD and CHD are structurally very similar which is a further indication for the finding that just one excited state is involved in the dynamics of CHD.One of the major obstacles for previous investigations of the dynamics of CHD was to decipher the existence and the quantum yields of the unsuccessful pathway 12,14,15. Here, we see a clear indication that this pathway exists by comparing experiment with theory: As indicated in the previous section, the photoelectron spectrum of the unsuccessful trajectories…”

mentioning

confidence: 77%

“…Cyclohexa-1,3-diene (CHD) is one of the most thoroughly studied molecules in time resolved photoexcitation experiments [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and ab initio computations 9,15,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and is the subject of two recent reviews. 32,33 The large interest originally stems from CHD being the prototype for a pericyclic reaction used to explain the Woodward-Hoffmann rules.…”

Section: Introductionmentioning

confidence: 99%

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Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

et al. 2016

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We have reinvestigated the excited state dynamics of cyclohexa-1,3-diene (CHD) with time-resolved photoelectron spectroscopy and fewest switches surface hopping molecular dynamics based on linear response time-dependent density functional theory after excitation to the lowest lying ππ* (1B) state. The combination of both theory and experiment revealed several new results: First, the dynamics progress on one single excited state surface. After an incubation time of 35 ± 10 fs on the excited state, the dynamics proceed to the ground state in an additional 60 ± 10 fs, either via a conrotatory ring-opening to hexatriene or back to the CHD ground state. Moreover, ring-opening predominantly occurs when the wavepacket crosses the region of strong nonadiabatic coupling with a positive velocity in the bond alternation coordinate. After 100 fs, trajectories remaining in the excited state must return to the CHD ground state. This extra time delay induces a revival of the photoelectron signal and is an experimental confirmation of the previously formulated model of two parallel reaction channels with distinct time constants. Finally, our simulations suggest that after the initially formed cis-Z-cis HT rotamer the trans-Z-trans isomer is formed, before the thermodynamical equilibrium of three possible rotamers is reached after 1 ps.

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mentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

et al. 2016

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“…(3) and then combined with a ratio of 1:0.8. (The initial population of 3p x , 3p y , and 3p z states for 200 nm excitation has previously been determined to be 1:0.8:0 from both an oscillator strength calculation 26 and an intensity analysis of photoelectron spectra 27 ).…”

Section: Methodsmentioning

confidence: 99%

“…This carries a number of advantages in terms of the goals of our experiment. First, the 3p electronic state has a comparatively long lifetime of about 200 fs, as measured by photoelectron spectroscopy 26,27 . Second, the initial changes in molecular geometry are minor, which ensures that these do not obscure the redistribution of the electrons in the observed signal.…”

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confidence: 99%

Observation of the molecular response to light upon photoexcitation

et al. 2020

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When a molecule interacts with light, its electrons can absorb energy from the electromagnetic field by rapidly rearranging their positions. This constitutes the first step of photochemical and photophysical processes that include primary events in human vision and photosynthesis. Here, we report the direct measurement of the initial redistribution of electron density when the molecule 1,3-cyclohexadiene (CHD) is optically excited. Our experiments exploit the intense, ultrashort hard x-ray pulses of the Linac Coherent Light Source (LCLS) to map the change in electron density using ultrafast x-ray scattering. The nature of the excited electronic state is identified with excellent spatial resolution and in good agreement with theoretical predictions. The excited state electron density distributions are thus amenable to direct experimental observation.

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“…The interconversion between CHD and HT is an important model for electrocyclic reactions, and its motif is used in the synthesis of vitamin D in the skin upon exposure to sunlight 35 . The CHD/HT system is favorable for the present investigation because optical excitation at 200 nm is followed by a rapid electronic relaxation that dominantly leads to the vibrationally hot CHD in the ground electronic state 36 . The resulting molecules are very hot (~2870 K for CHD, assuming harmonic frequencies reported by Autrey et al 37 ), and undergo a thermal ring-opening reaction to HT.…”

Section: Introductionmentioning

confidence: 99%

Scattering off molecules far from equilibrium

Yong

Ruddock

Stankus

et al. 2019

The Journal of Chemical Physics

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Pump-probe gas phase X-ray scattering experiments, enabled by the development of Xray Free Electron Lasers, have advanced to reveal scattering patterns of molecules far from their equilibrium geometry. For polyatomic molecular systems, large amplitude vibrational motions are associated with anharmonicity and shifts of interatomic distances (known as the 'shrinkage effect' in linear molecules), making analytical solutions using traditional harmonic approximations inapplicable. More generally, the interatomic distances in a polyatomic molecule are not independent and the traditional equations commonly used to interpret the data may give unphysical results. Here we introduce a novel method based on molecular dynamic trajectories and illustrate it on two examples of hot, vibrating molecules at thermal equilibrium. When excited at 200 nm, 1,3cyclohexadiene (CHD) relaxes on a sub-picosecond time scale back to the reactant molecule, the dominant pathway, and to various forms of 1,3,5-hexatriene (HT). With internal energies of about 6 eV, the energy thermalizes quickly, leading to structure distributions that deviate significantly from their vibrationless equilibrium. The experimental and theoretical results are in excellent agreement and reveal that a significant contribution to the scattering signal arises from transition state structures near the inversion barrier of CHD. In HT, the analysis clarifies that previous inconsistent structural parameters determined from electron diffraction were artifacts resulting from the use of inapplicable analytical equations.

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Ultrafast Dynamics of 1,3-Cyclohexadiene in Highly Excited States

Cited by 13 publications

References 27 publications

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

Observation of the molecular response to light upon photoexcitation

Scattering off molecules far from equilibrium

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