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Anion Electronic Structure and Correlated, One-electron Theory

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Anion Electronic Structure and Correlated, One-electron Theory

J. V. Ortiz

Department of Chemistry and Biochemistry

Auburn University

www.auburn.edu/cosam/JVOrtiz

Workshop on Molecular Anions and Electron-Molecule Interactions in Honor of

Professor Kenneth Jordan

July 1, 2007

Park City, Utah

Funding

National Science Foundation

Defense Threat Reduction Agency

- Symposium Organizers
- Jack Simons
- Brad Hoffman

- Auburn University
- Department of Chemistry and Biochemistry

- Auburn Coworkers

- UNAM Collaborators:
- Ana Martínez
- Alfredo Guevara

Deductive agenda:

Deduce properties of molecules from quantum mechanics

Calculate chemical data, especially if experiments are difficult or expensive

Inductive agenda:

Identify and explain patterns in structure, spectra, energetics, reactivity

Deepen and generalize the principles of chemical bonding

G. N. Lewis

E. Schrödinger

Electron Propagator

Theory

Exactness

Interpretation

Molecular Orbital

Theory

Applications

Hartree Fock Theory

Hartree Fock Equations:

(Tkin + Unucl + JCoul - Kexch)φiHF ≡

F φiHF=εiHF φiHF

Same potential for all i:

core, valence, occupied, virtual.

εiHF includes Coulomb and exchange contributions to IEs and EAs

Electron Propagator Theory

Dyson Equation:

[F + ∑(εiDyson)]φiDyson = εiDyson φiDyson

Self energy, ∑(E): Energy dependent, nonlocal potential that varies for each electron binding energy

εiDyson includes Coulomb, exchange, relaxation and correlation contributions to IEs and EAs

φiDyson describes effect of electron detachment or attachment on electronic structure

- Electron Detachment (IEs)
φiDyson(x1) =

N-½∫ΨN(x1,x2,x3,…,xN)Ψ*i,N-1(x2,x3,x4,...,xN)

dx2dx3dx4…dxN

- Electron Attachment (EAs)
φiDyson(x1) =

(N+1)-½∫ Ψi,N+1(x1,x2,x3,...,xN+1)Ψ*N(x2,x3,x4,…,xN+1) dx2dx3dx4…dxN+1

- Pole strength
Pi = ∫|φiDyson(x)|2dx

0 ≤ Pi ≤ 1

Electron Correlation

Dyson Orbital

Canonical MO

Correlated Electron

Binding Energy

Orbital Energy

Integer Occupation

Numbers

Pole Strengths

Independent-Particle

Potential

Energy-dependent,

Self-Energy

- Does electron propagator theory offer a solution to Mulliken’s dilemma?

The more accurate the

calculations become,

the more the concepts

vanish into thin air.

- R. S. Mulliken

Uracil

π1

σ-

π2

σ+

π3

Thymine

Methyl (CH3) participation

- Methyl group destabilizes π orbitals with large amplitudes at nearest ring atom
- Therefore, IE(T) < IE(U)
- Valid principles for substituted DNA bases, porphyrins and other organic molecules

- Neglect off-diagonal elements of Σ(E) in canonical MO basis: φiDyson(x) = Pi½φiHF-CMO(x)
- Partial summation of third-order diagrams
- Arithmetic bottleneck: oN4 (MP2 partial integral transformation)
- Storage bottleneck: o2v2 in semidirect mode
- Abelian, symmetry-adapted algorithm in G03

ΣP3pq(E) =

½Σiab <pi||ab><ab||qi> Δ(E)-1iab +

½Σaij <pa||ij>(<ij||qa> + Wijqa) Δ(E)-1aij +

½Σaij Upaij(E)<ij||qa>Δ(E)-1aij

where

Δ(E)-1pqr = (E + εp – εq – εr)-1

Wijqa = ½Σbc<bc||qa><ij||bc> Δ-1ijbc

+ (1-Pij)Σbk<bi||qk><jk||ba> Δ-1jkab

Upaij(E) = - ½Σkl<pa||kl><kl||ij> Δ(E)-1akl

- (1 – Pij) Σbk<pb||jk><ak||bi> Δ(E)-1bjk

- 31 Valence IEs of Closed-Shell Molecules:
(N2,CO,F2,HF,H2O,NH3,C2H2,C2H4,CH4,HCN,H2CO)

MAD (eV) = 0.20 (tz)

- 10 VEDEs of Closed-Shell Anions:
(F-,Cl-,OH-,SH-,NH2-,PH2-,CN-,BO-,AlO-,AlS-)

MAD (eV) = 0.25 (a-tz)

- Arithmetic bottleneck: o2v3 for Wijqa
- Storage bottleneck: <ia||bc> for Wijqa

Input to Gaussian 03

# OVGF 6-311G** iop(9/11=10000)

P3 Electron Propagator for Water

0 1

O

H 1 0.98

H 1 0.98 2 105.

Available diagonal approximations for Σ(E):

Second order, Third order, P3, OVGF (versions A, B & C)

- Nucleotides: phosphate-sugar-base DNA fragments
- Electrospray ion sources
- Magnetic bottle detection
- High resolution laser spectroscopy of ions, mass spectrometry
- Goal: predict photoelectron spectra of anionic nucleotides (vertical electron detachment energies or VEDEs)

DAMP

Anomalous peak for dGMP

Base = adenine

DCMP

G: lowest IE

of DNA bases

Base = cytosine

DGMP

Base = guanine

Dyson orbitals for

lowest VEDEs:

phosphate or base?

DTMP

Base = thymine

L-S.Wang, 2004

0 kcal/mol

4.62

4.66

0 kcal/mol

5.1

9.2

- DGMP: G amino to Phosphate oxygen
- DAMP: Sugar hydroxy to Phosphate oxygen

- Phosphate anion reduces Base VEDEs by several eV
- Base also increases Phosphate VEDEs
- Therefore, Base and Phosphate VEDEs
are close

- Differential correlation effects are large
- Koopmans ordering is not reliable

ΣP3+pq(E) =

½Σiab <pi||ab><ab||qi> Δ(E)-1iab +

[1+Y(E)]-1 ½Σaij<pa||ij>(<ij||qa> + Wijqa) Δ(E)-1aij + ½Σaij Upaij(E)<ij||qa>Δ(E)-1aij

where

Y(E) = {-½Σaij<pa||ij>Wijqa Δ(E)-1aij} {½Σaij<pa||ij><ij||qa> Δ(E)-1aij}-1

- 31 Valence IEs of Closed-Shell Molecules:
(N2,CO,F2,HF,H2O,NH3,C2H2,C2H4,CH4,HCN,H2CO)

MAD (eV) = 0.19 (tz), 0.19 (qz)

- 10 VEDEs of Closed-Shell Anions:
(F-,Cl-,OH-,SH-,NH2-,PH2-,CN-,BO-,AlO-,AlS-)

MAD (eV) = 0.11 (a-tz), 0.13 (a-qz)

- Wang: first anion photoisomerization
- Jarrold: Al3O3-(H2O)n photoelectron spectra n=0,1,2
- Distinct profile for n=1
- Similar spectra for n=2 and n=0

Book

Kite

Al3O3-

Al3O4H2-

Al3O5H4-

- Need better reference orbitals for:
diradicaloids, bond dissociation, unusual bonding …

- Generate renormalized self-energy with approximate Brueckner reference determinant

- Asymmetric Metric:
(X|Y)=

<Brueckner|[X†,Y]+(1+T2)|Brueckner>

- Galitskii-Migdal energy =
BD (Brueckner Doubles, Coupled-Cluster)

- Operator manifold: f~a†aa=f3
- Discard only 2ph-2hp couplings

- Vertical Electron Detachment Energies of Anions: MAD=0.03 eV
- 1s Core Ionization Energies: MAD = 0.2%
- Valence IEs of Closed-Shell Molecules:
MAD = 0.15 eV

- IEs of Biradicaloids: MAD = 0.08 eV

B: Mysterious low-VEDE peak

Not due to hot NH4-

Variable relative intensity

Another isomer of NH4-?

A: H- detachment

with vibrational

excitation of NH3

X: H-(NH3)

NH3 increases H- VEDE

X

B

x300

A

Hydride anion: H-

H-(NH3) constituents:

Ammonia molecule: NH3

Lewis: 1 electron pair

H nucleus has 1+ charge

Negative charge attracts

+ end of polar NH bond

Lewis: 3 electron pairs

shared in polar NH bonds

+ 1 unshared pair on N

→

Partial + charge on H’s

Partial – charge on N

Anion(molecule)

structure

accounts for

dominant peaks

Idea: NH2-(H2) anion-molecule complex

Reject: spectral peak would be high-VEDE, not low

Idea: NH4- has 5 valence e- pairs

Deploy in 4 N-H bonds and 1 unshared pair

at the 5 vertices of a trigonal biprism or

square pyramid

Calculations find no such structures!

Instead, they spontaneously rearrange ….

Tetrahedral NH4- has 4

equivalent N-H bonds

Defies Lewis theory

Defies valence shell

electron pair

repulsion theory

Structure similar to that of NH4+

So where are the 2 extra electrons?

Predicted VEDEs from Electron Propagator Theory

for Anion(molecule) and Tetrahedral forms of NH4-

coincide with peaks from photoelectron spectrum

H-(NH3) has 2 electrons

in hydride-centered orbital

with minor N-H delocalization.

VEDE is 1.07 eV

Tetrahedral NH4- has 2

diffuse electrons located

chiefly outside of NH4+ core.

VEDE is 0.47 eV

Energy (au)

Intrinsic Reaction Coordinate

- Highly correlated motion of two diffuse (Rydberg) electrons in the field of a positive ion (NH4+ , OH3+)
- United atom limit is an alkali anion: Na-
- Extravalence atomic contributions in Dyson orbitals

NH4-

OH3-

Eact = 5.1

Erx = -39.9

X: H-(NH3)2 e- detachment

B & C: two low EBEs!

C

B

X

x500

A

- H-(NH3)2 anion-
molecule complex

- NH4-(NH3) anion-
molecule complex

with tetrahedral NH4-

- N2H7- with hydrogen bond (similar to N2H7+ )

H-(NH3)2 has hydride centered Dyson orbital

EPT predicts 1.49 eV for VEDE

Peak observed in spectrum at 1.46 ± 0.02 eV

Dyson orbital concentrated near NH4-

EPT predicts 0.60 eV for VEDE

Peak observed at 0.58 ± 0.02 eV

Dyson orbital concentrated near 3 hydrogens

EPT predicts 0.42 eV for VEDE

Peak observed at 0.42 ± 0.02 eV

- (NH4-)(NH3)2 : 0.66 (Expt.) 0.68 (EPT)
- (N2H7-)(NH3) : 0.49 (Expt.) 0.49 (EPT)
- (N3H10-) : 0.42 (Expt.) 0.40 (EPT)

x800

Molecule-Hydride

Bridge

Ion-dipole

H-(H2O)2 VEDE: 2.36 eV

H-bridged VEDE: 0.48 eV

Ion-dipole VEDE: 0.74 eV

Chemical bonds arise

from pairs of electrons

shared betweenatoms

G.N. Lewis

I. Langmuir

W.N. Lipscomb

Unshared pairs

localized on single atoms

affect bond angles

Molecular cations may

bind an e- pair peripheral

to nuclear framework:

Double Rydberg Anions

R.J. Gillespie

R.S. Nyholm

- Deductive, quantitative theory:
Prediction and interpretation enable dialogue with experimentalists requiring accurate data

- Inductive, qualitative theory:
Orbital formalism generalizes and deepens qualitative notions of electronic structure, relating structure, spectra and reactivity