quantum dynamics of electronically excited molecules ... · photophysics/chemistry of phenol and...
TRANSCRIPT
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Quantum Dynamics of Electronically Excited Molecules:Current Developments and Future Challenges
Susanta Mahapatra
School of ChemistryUniversity of Hyderabad, Hyderabad 500046
Email: [email protected], Tel: +91-40-23134826; URL: http://172.16.56.51/~sm/
Indo-German workshop, September 7-8, 2009, Neuss, Germany
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Central Theme
Entanglement electronic and nuclear motion in molecules;ubiquitous, dynamics of excited electronic states of
Polyatomic Molecules
Crossings of electronic potential energy surfacesNuclear motion is quantum mechanical
A central quest in the new vista of chemical dynamics
Electron-Nuclear Coupling f
hγ
i
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Noncrossing Rule : von Neumann and Wigner
“Electronic states of a diatomic molecule do not cross, unless permitted by symmetry”
J. von Neumann and E. Wigner, Physik. Z. 30, 467 (1929)E. Teller, J. Phys. Chem. 41, 109 (1937)Landau & Lifshitz, Quantum Mechanics: Nonrelativistic Theory, 1965H. C. Longuet Higgins, Proc. R. Soc. (London) Ser. A 344, 147 (1975)G. Herzberg and H. C. Longuet Higgins, Discuss. Faraday Soc. 35, 77 (1963)C. A. Mead, J. Chem. Phys. 70, 2276 (1979)
It does not apply to Polyatomic systems !!
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Diabatic (?)
Equation of a ellipticalDouble – cone
Adiabatic (?)
Surfaces are degenerate when Δ2 = 0 ; H12
2 = 0
This happens when these terms are independent i.e. they are function of different coordinates
Λ = Linear coupling vector δ = Gradient difference vector
Review of basic concepts
Coordinates
X1=X2=0
22
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Diatomics : Only one coordinate
• If the two states have same symmetry they do not crossNon crossing rule
• If the states have different symmetry then H12 = 0 ; they can cross
Polyatomics : Degrees of freedom n > 1
• States can always cross in principle, irrespective of symmetry
Near the degeneracy
Degeneracy is lifted to first – order in the space spanned by the vectors δ and λ
Δ = δ·RH12 = λ·R
J. von Neumann and E. Wigner, Physik. Z. 30, 467 (1929);C. A. Mead, J. Chem. Phys. 70, 2276 (1979)
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n-2 dimensional intersection space
2 dimensional branching space
x2
x1
Conical Intersection Glancing Intersection
For linear systems
Crucial: paradigm forsignaling ULTRAFASTdecay of excited molecularstates
Intersections of molecular potential energy surfaces
Consequences:Break-down of the Born-Oppenheimer approximation
Nuclear motion no longer remain confined on a (scalar) adiabatic PES
a nonadiabatic situation
Herzberg & Teller, Z. Phys. Chemie B21, 410 (1933);E. Renner, 92, 172 (1934)
Teller, J Phys. Chem. 41, 109 (1937);Herzberg & Longuet-Higgins, Discuss. Faraday Soc. 35, 77 (1963);Carrington, ibid. 53, 27 (1972)
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H11 H12
H21 H22Smooth
cusp
Lichten, Phys. Rev. 131, 229 (1963); Smith, Phys. Rev. 179, 111 (1969)
Adiabatic Diabatic
Complexities in Theoretical Treatments:Singular nonadiabatic coupling terms in the adiabatic representation
Quite Tricky!
Derivative coupling vector
Born-Huang term
Adiabatic electronic wavefunction changes signTopological effect / Geometric phase effect
G. Herzberg and H. C. Longuet-Higgins, Discuss. Faraday Soc. 35, 77 (1963)H. C. Longuet-Higgins, Proc. Roy. Soc. London, Ser. A, 344, 147 (1975)M. V. Berry, Proc. R. Soc. London, Ser. A 392, 45 (1984)C. A. Mead, Rev. Mod. Phys. 64, 51 (1992)
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Construction of theoretical models and algorithms
ab initio electronic structure calculations and quantum dynamical simulations
Indo-German Collaborations: Highlights
Traditional wave packet and also MCTDHMatrix diagonalization
1. Conical intersections in H3
2. The Jahn-Teller and pseudo-Jahn-Teller effects in the radical cations of cyclopropane and methyl fluoride
3. Photophysics/chemistry of phenol and pyrrole
4. Photodetachment spectroscopy of NO3-
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“All non-linear nuclear configurations are unstable on an orbitally degenerate electronic state”
“Tend to distort in such a way as to remove the electronic degeneracy” ---- H. A. Jahn & E. Teller 1937
Energy levels cross at E0
Four fold axial symmetry reduces to two foldEσ (I) = Eσ ′ (II)Eσ (II) = Eσ ′ (I)
Eσ Eσ ′
Eσ ′Eσ
III
The Jahn-Teller effect
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γ
r
R
H H
H
JT Interactions in the Electronic Ground State of H3
DMBE PES: Varandas et al. J. Chem. Phys. 86, 6258 (1987).
Vcmin = 2.74 eV
D3h
Adiabatic to diabatic transformation angle
H + H2 H2 + H
V+
V-
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A1 eQx Qy
χ
Qy
Qx
Pseudorotation angle
R
H3 Vibrations:
S. Mahapatra and H. Köppel, J. Chem. Phys. 109, 1721 (1998).A. Thiel and H. Köppel, J. Chem. Phys. 110, 9371 (1999).
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Large shift from the vertical transition energy Huge ZPE (~ 0.7 eV) due to the cusp of the JT split PESs
Crossing at E = 3.089 eV (Vc min = 2.74 eV)
wave packet terminates at the immediate neighborhood of the conical intersections of the final electronic state.
~ 1.2 eV
~ 2.95 eV ~ 4.15 eVV- V+
R. Bruckmeier, Ch. Wunderlich, and H. Figger. Phys. Rev. Lett. 72 2550 (1994)Mahapatra and Köppel, Phys. Rev. Lett. 81, 3116 (1998);
J. Chem. Phys. 109, 1721 (1998); Faraday Discuss, 110, 248 (1998)
Theory Time-dependent Wave Packet
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Nonradiative decay How fast ?
Time-dependent electronic population ofthe upper adiabatic ( V+ ) sheet
To within 3-6 fs.
Perhaps the fastest femtosecond decay process treated in the literature !!
Mahapatra and Köppel, Phys. Rev. Lett. 81, 3116 (1998)
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Dissociative Recombination (DR) of H3
DR mechanism is complex and not yet understood
Various nonadiabatic transitions are anticipated to contribute to the observed DR rate
DR mechanism is important to the interstellar chemistry
Rydberg electronic states are coupled to the ground electronic state in the DR process
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Jahn-Teller conical intersections in 3p (E′) and 3d (E″)
The Rydberg excited H3 undergoes various nonadiabatictransitions and dissociates on the repulsive lower adiabaticsheet of its ground electronic state
Study of JT CIs is important in understanding the DR processes
The (E⊗e)-JT CIs in these electronic states influencethe nuclear dynamics in the DR processes
• Static aspects are studied in terms of ab initio quantum chemistry calculations
• Dynamic aspects are studied in terms of vibronic spectra and nonradiative decay behavior of these electronic states
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3p (E′)
3d (E″)
Potential energy surfaces PES Contours
SplineRaw
M. Jungen and coworkers, Khim. Fiz., 23(2), 71 (2004)Rao, Mahapatra, Köppel, Jungen, J. Chem. Phys. 123, 134325 (2005)
JT interactions are low in 3d (E′)
JT CIs in 3p (E′)
JT CIs in 3d (E″)
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Vibronic Coupling Model :
E10
E20
E30
Harmonic
κN
KÖppel, Domcke and Cederbaum, Adv. Chem. Phys. 57, 59, (1984);
Hamiltonian to be invariant under the symmetry operation of the corresponding point group
Determines the relative signs of the coupling constants
Parameters are obtained by computing potential energy surfaces
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Dynamical Observables
Multi-Configuration Time-Dependent Hartree (MCTDH) scheme
Meyer, Manthe, Cederbaum, Chem. Phys. Lett. 165, 73 (1990); Meyer, Manthe, Cederbaum, Chem. Phys. 97, 3199 (1992); Beck, Jäckle, Worth, Meyer, Phys. Rep. 324, 1 (2000).
Worth, Beck, Jäckle, Meyer, The MCTDH Package, Version 8.2, 2000, University of Heidelberg, Germany.Mayer, Version 8.3, 2002. See http://www.pci.uni-heidelberg.de/tc/usr/mctdh/
The photoelectron spectrumFermi’s golden rule:
of the autocorrelation function
Nonradiative decay of electronic populations
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Jahn-Teller and pseudo-Jahn-Teller effects in cyclopropane radical cationCyclopropane Radical Cation
MP2/cc-PVTZ Expt.
rC-C 1.50378 A° 1.499rC-H 1.07834 A° 1.074
∠CCC 60 59.98∠HCH 115.081 117.08
2.43 eV
2.59 eV
X 2E ′~
A 2E”~
B 2A1′~E
Eqm. Geometry : D3h
+
0.78
Holland et. al. J. Elect. Spect. 125, 2002, 57-68
Γvib =3A1′+A2′+4E′+A1′′ +2A2′′ +3E′′
[E′ Χ E′]† = [E′′ Χ E′′]† = A′1 +E′
[E′ Χ E′′] =A1′′ + A2′′ +E′′
JT Active
Pseudo- JT Active
Condon Active
Mean Spacing≈ 60.0 meV
D3h
hγ
(E⊗e) -JT
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Important vibrational modes
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Adiabatic Potential Energy cuts of X2E′ - A2E′′ electronic manifold
Symmetric modes Degenerate modes
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X2E' band of CP+: LVC Model
0.15 eV ν1
0.19 eV ν2
0.113 eV ν4
0.131 eV ν5
T. S. Venkatesan et. al, J. Phys. Chem. A 108 2256 (2004)
ΔEJT = 0.98 eV
0.80 eV
Expt
Theory (Sym ⊗ JT)
0.78 eV
Vcmin = 10.64 eV
V0- = 9.66 eV
Slonczewski resonances
J.C.Slonczewski, Phys. Rev. 131,1596 (1963)
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X2E’ band of CP+
0.81 eV
0.80 eV
Linear vibronic coupling
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Dominant progressions due to υ2, υ3, υ4, and υ6 vibrational modes
A2E" band of CP+ (LVC Model)
ΔEJT = 0.638 eV
υ2 190 meV
υ3 396 meV
υ6 187 meV
υ4 122 meV
Irregular spacingis due to multimodeJT effect.
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T. S. Venkatesan et. al, J. Phys. Chem. A, 111, 1746 (2007); J. Mol. Struct. 838, 100 (2007).
4 states and 14 modes quadratic JT plus linear PJT model.
Huge impact of PJTcoupling via a1
” and e”
vibrational modes
Vibronic Spectrum of Coupled X2E’-A2E” Manifold
VPJT (min) = 12.12 eV ~ 1.47eV above and ~ 0.62 eV below the minimum of X and A JT conical intersections.
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Vibronic Coupling in Methyl Halides
Cation
~ 4.81eV
Mode Frequency/ eV Descriptionν1(A1) 0.1336 C-F Stretchν2(A1) 0.1865 CH3 Bendν3(A1) 0.3822 C-H Stretchν4(E) 0.1503 C-F Bendν5(E) 0.1893 CH3 Deformationν6(E) 0.3950 C-H Stretch
C
F
HH(C3V)
B2EA2A1~~
X2E~ H
17.15617.127
13.318
Γvib = 3A1+3E[E x E] = A1+ E
Condon ActiveJT + PJT Active
Karlsson et al. Phys. Scrip. 16, 225 (1977)
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CH3F+
Adiabatic Potential Energy Surface CASSCF/MRCI ; aug-cc-pVTZ with ECP for Fluorine CAS (11,16)
Mahapatra, Vallet, Woywod, Köppel and Domcke, Chem. Phys. 304, 17 (2004).
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Vibronic Structure of the X 2E State ∼
Linear Model Quadratic Model
Sym Sym∼ 0.129
0.185ν1ν2(Very weak)
JT0.19
0.15ν5ν4
Sym ⊗ JTν1+ν4+ν5
∼ 0.104
ν1ν2 (Very weak)
γ ≈- 0.024
JTν5+ ν4
Sym ⊗ JT
CH3F+
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X 2E Band ∼CH3F+
JT + PJT
Expt
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Vibronic Structure of the B 2E State∼
Linear Model Quadratic Model
Sym Sym
JT JT
Sym ⊗ JT Sym ⊗ JT
ν1 + ν3 (weak)
ν5 + ν6 (weak)
ν1 + ν5
γν 1 = 0.055γν 3 = 0.023
γν 6 = 0.0102
η ∼ 10-3 or less
CH3F+
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CH3F+
A 2A1 + B 2E Band∼ ∼
JT + PJT
Expt
B2E + A2A1(2 : 1)
∼ ∼
CP, 304, 17 (2004)
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Impact of the intermode (a1-e) bilinear coupling terms
Mahapatra, Vallet, Woywod, Koeppel and Domcke, J. Chem. Phys. 123, 231103 (2005)
Schmidt-Kluegmann, Koeppel, Schmatz and Botschwina, Chem. Phys. Lett. 369, 21 (2003)
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Photostability & nonadiabatic transitions
HO
Photochemistry of DNA building blocks: chromophores
• Extremely low quantum yield of fluorescence of the strongly UV absorbing excited singlet ππ*state
• Very fast nonradiative processes
Conversion back to the ground state
hγ
Photochemical Funnel
• The photon energy quickly dissipated before more profound chemical rearrangements Photostability
Upper diabaticLower diabatic
Faraday Discuss. 127, 283 (2004)J. Chem. Phys. 122, 224315 (2005)
123, 144307 (2005)
J. Photochem. Photobio. A 190, 177 (2007)
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• 1πσ* Optically dark Two curve crossings which become conicalintersections when out-of-plane modes (e.g. CCOH dihedral angle) are considered
• Both CIs have same coupling coordinate CCOH dihedral angle θ (torsion)
• The photo induced dynamics is simulated by time-dependent WP method
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Wave packet dynamics
P1
P2
P3
S0
1ππ*1πσ* Diabatic
Upper diabaticLower diabatic
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Acknowledgement
Funding:
DST, CSIR-New DelhiVWS and AvH Stiftung, Germany
Computational Facilities:CMSD, University of Hyderabad
Dr. R. PadmanabanDr. T. S. VenkatesanDr. S. GhosalMr. B. Jayachander RaoMr. V. Sivaranjana ReddyMr. T. MondalMr. S. GhantaMr. T. Rajagopala RaoMr. S. Rajagopala ReddyMr. T. Roy
Coworkers:
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