On the description of conical intersections—A continuous representation of the local topography of seams of conical intersection of three or more electronic states: A generalization of the two state result

2014 ◽  
Vol 141 (17) ◽  
pp. 174109 ◽  
Author(s):  
Xiaolei Zhu ◽  
David R. Yarkony
Keyword(s):  
Electronic States ◽  
Conical Intersection ◽  
Continuous Representation ◽  
Conical Intersections ◽  
State Result ◽  
Local Topography

scholarly journals Visualizing conical intersection passages via vibronic coherence maps generated by stimulated ultrafast X-ray Raman signals

2020 ◽  
Vol 117 (39) ◽  
pp. 24069-24075
Author(s):  
Daniel Keefer ◽  
Thomas Schnappinger ◽  
Regina de Vivie-Riedle ◽  
Shaul Mukamel
Keyword(s):  
Laser Pulse ◽  
Free Electron Laser ◽  
Electronic States ◽  
Optical Excitation ◽  
Time Dependent ◽  
Conical Intersection ◽  
Energy Splitting ◽  
Conical Intersections ◽  
Strongly Coupled ◽  
X Ray

The rates and outcomes of virtually all photophysical and photochemical processes are determined by conical intersections. These are regions of degeneracy between electronic states on the nuclear landscape of molecules where electrons and nuclei evolve on comparable timescales and thus become strongly coupled, enabling radiationless relaxation channels upon optical excitation. Due to their ultrafast nature and vast complexity, monitoring conical intersections experimentally is an open challenge. We present a simulation study on the ultrafast photorelaxation of uracil, based on a quantum description of the nuclei. We demonstrate an additional window into conical intersections obtained by recording the transient wavepacket coherence during this passage with an X-ray free-electron laser pulse. Two major findings are reported. First, we find that the vibronic coherence at the conical intersection lives for several hundred femtoseconds and can be measured during this entire time. Second, the time-dependent energy-splitting landscape of the participating vibrational and electronic states is directly extracted from Wigner spectrograms of the signal. These offer a physical picture of the quantum conical intersection pathways through visualizing their transient vibronic coherence distributions. The path of a nuclear wavepacket in the vicinity of the conical intersection is directly mapped by the proposed experiment.

Controlled intramolecular H-transfer in malonaldehyde in the electronic ground state mediated through the conical intersection of 1nπ* and 1ππ* excited electronic states

2019 ◽  
Vol 21 (36) ◽  
pp. 20018-20030 ◽  
Author(s):  
K. R. Nandipati ◽  
Arun Kumar Kanakati ◽  
H. Singh ◽  
S. Mahapatra
Keyword(s):  
Ground State ◽  
Electronic States ◽  
Laser Pulses ◽  
Electronic Ground State ◽  
Conical Intersection ◽  
Uv Laser ◽  
Excited Electronic States ◽  
Electronic Ground

We report photo-isomerization of malonaldehyde in its electronic ground state (S0), mediated by coupled 1nπ*(S1)–1ππ*(S2) excited electronic states, accomplished with the aid of optimally designed ultraviolet (UV)-laser pulses.

scholarly journals Dissipative dynamics at conical intersections: simulations with the hierarchy equations of motion method

2016 ◽  
Vol 194 ◽  
pp. 61-80 ◽  
Author(s):  
Lipeng Chen ◽  
Maxim F. Gelin ◽  
Vladimir Y. Chernyak ◽  
Wolfgang Domcke ◽  
Yang Zhao
Keyword(s):  
Relaxation Time ◽  
Electronic State ◽  
Equations Of Motion ◽  
Equation Of Motion ◽  
Harmonic Oscillators ◽  
Conical Intersection ◽  
Coherent Motion ◽  
Conical Intersections ◽  
Dissipative Dynamics ◽  
Motion Method

The effect of a dissipative environment on the ultrafast nonadiabatic dynamics at conical intersections is analyzed for a two-state two-mode model chosen to represent the S2(ππ*)–S1(nπ*) conical intersection in pyrazine (the system) which is bilinearly coupled to infinitely many harmonic oscillators in thermal equilibrium (the bath). The system–bath coupling is modeled by the Drude spectral function. The equation of motion for the reduced density matrix of the system is solved numerically exactly with the hierarchy equation of motion method using graphics-processor-unit (GPU) technology. The simulations are valid for arbitrary strength of the system–bath coupling and arbitrary bath memory relaxation time. The present computational studies overcome the limitations of weak system–bath coupling and short memory relaxation time inherent in previous simulations based on multi-level Redfield theory [A. Kühl and W. Domcke, J. Chem. Phys. 2002, 116, 263]. Time evolutions of electronic state populations and time-dependent reduced probability densities of the coupling and tuning modes of the conical intersection have been obtained. It is found that even weak coupling to the bath effectively suppresses the irregular fluctuations of the electronic populations of the isolated two-mode conical intersection. While the population of the upper adiabatic electronic state (S2) is very efficiently quenched by the system–bath coupling, the population of the diabatic ππ* electronic state exhibits long-lived oscillations driven by coherent motion of the tuning mode. Counterintuitively, the coupling to the bath can lead to an enhanced lifetime of the coherence of the tuning mode as a result of effective damping of the highly excited coupling mode, which reduces the strong mode–mode coupling inherent to the conical intersection. The present results extend previous studies of the dissipative dynamics at conical intersections to the nonperturbative regime of system–bath coupling. They pave the way for future first-principles simulations of femtosecond time-resolved four-wave-mixing spectra of chromophores in condensed phases which are nonperturbative in the system dynamics, the system–bath coupling as well as the field-matter coupling.

scholarly journals Unveiling the spatial distribution of molecular coherences at conical intersections by covariance X-ray diffraction signals

2021 ◽  
Vol 118 (22) ◽  
pp. e2105046118
Author(s):  
Stefano M. Cavaletto ◽  
Daniel Keefer ◽  
Jérémy R. Rouxel ◽  
Flavia Aleotti ◽  
Francesco Segatta ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Three Dimensional ◽  
Laser Pulses ◽  
Conical Intersection ◽  
Conical Intersections ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
Diffraction Imaging ◽  
The Rich

The outcomes and timescales of molecular nonadiabatic dynamics are decisively impacted by the quantum coherences generated at localized molecular regions. In time-resolved X-ray diffraction imaging, these coherences create distinct signatures via inelastic photon scattering, but they are buried under much stronger background elastic features. Here, we exploit the rich dynamical information encoded in the inelastic patterns, which we reveal by frequency-dispersed covariance ultrafast powder X-ray diffraction of stochastic X-ray free-electron laser pulses. This is demonstrated for the photoisomerization of azobenzene involving the passage through a conical intersection, where the nuclear wave packet branches and explores different quantum pathways. Snapshots of the coherence dynamics are obtained at high frequency shifts, not accessible with conventional diffraction measurements. These provide access to the timing and to the confined spatial distribution of the valence electrons directly involved in the conical intersection passage. This study can be extended to full three-dimensional imaging of conical intersections with ultrafast X-ray and electron diffraction.

scholarly journals Conical intersection dynamics of pyrimidine nucleosides tracked with sub-20-fs UV pulses

2019 ◽  
Vol 205 ◽  
pp. 10007
Author(s):  
Rocío Borrego-Varillas ◽  
Artur Nenov ◽  
Lucia Ganzer ◽  
Aurelio Oriana ◽  
Irene Conti ◽  
...  
Keyword(s):  
Excited State ◽  
Numerical Simulations ◽  
Ab Initio ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Conical Intersection ◽  
Ultrafast Dynamics ◽  
Conical Intersections ◽  
Pyrimidine Nucleosides

By combining transient absorption spectroscopy with sub-20-fs UV pulses and ab initio numerical simulations we follow the ultrafast dynamics in pyrimidine nucleosides and visualize the passage through conical intersections presiding excited state deactivation.

Photodissociation pathways and conical intersections in the low‐lying electronic states of SiH+2

1994 ◽  
Vol 101 (12) ◽  
pp. 10576-10601 ◽  
Author(s):  
Steve P. Mort ◽  
Neville A. Jennings ◽  
Gabriel G. Balint‐Kurti ◽  
David M. Hirst
Keyword(s):  
Electronic States ◽  
Conical Intersections

The role of pyrimidine nucleobase excimers in DNA photophysics and photoreactivity

2009 ◽  
Vol 81 (9) ◽  
pp. 1695-1705 ◽  
Author(s):  
Israel González-Ramírez ◽  
Teresa Climent ◽  
Juan José Serrano-Pérez ◽  
Remedios González-Luque ◽  
Manuela Merchán ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Quantum Chemical ◽  
Electronic States ◽  
Conical Intersections ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Dna Nucleobases ◽  
Surface Crossings

Quantum chemical studies using the accurate CASPT2//CASSCF procedure show that π-stacked interactions in biochromophores such as pyrimidine (Pyr) DNA/RNA nucleobases pairs yield excimer-like situations which behave as precursors of processes like charge transfer (CT) or photoreactivity and are the source of the emissive properties in DNA. Examples are the CT between adjacent DNA nucleobases in a strand of oligonucleotides and the photodimerization taking place in cytosine (C) pairs leading to cyclobutanecytosine (CBC) mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersections (CIs) and other surface crossings between different electronic states.

Sign in / Sign up

Export Citation Format

Share Document