the negative ion photoelectron spectra of mov and crv presentedby beau barker
TRANSCRIPT
The Negative Ion The Negative Ion Photoelectron Photoelectron
SpectraSpectra of of
MoV and CrV MoV and CrVPresentedPresented
byby
Beau BarkerBeau Barker
Introduction
Ground states:
V 4s23d3 Cr 4s13d5 Mo 5s14d5
Early transition metal dimers are of interest because d-electrons are involved in bonding.
The d-orbitals are large enough to participate in bonding.
Dimers containing later transition metals, such as CrCu, Cu2 or Ni2, are dominated by s bonding.
Cr
Mo
W
V
Nb
Ta
Group 6Group 5
NPES Basics: Electron Kinetic Energy (eKE) Electron Binding Energy (eBE)
Experiments involve the use of the photoelectric effect:
The eKE is measured and the eBE found from the difference in energy between the eKE and the photon:
eBE is equal to the difference in energy between the anion and neutral states:
h eKE = eBE
M- + h M + e-
eBE = EElec + EVib + ERot
NPES Basics : Selection Rules
Electronic State Transitions:
For example: If anion is a doublet the neutral could be either a singlet or triplet.
Vibrational Transitions:
Intensities of vibrational transitions are governed by Franck-Condon overlap between the anion and neutral species.
S ±1
ion(q'')|neut(q')>|2
NPES Basics : Information from SpectraElectron affinity: The energy difference between the
ground states of the anion and neutral.
Vibrational frequencies: Found for both anion and neutral species.
Anharmonicities: If known accurately these can also yield bond dissociation energies (for diatomics).
Geometry Changes: Only the changes in equilibrium geometry are found between anion and neutral.
Orbitals: Bonding characteristics of the detached electron.
Anion Photoelectron Spectrometer
Ion-molecule Reactor"Flow Tube" Sector Magnet
Interaction Region
Argon-Ion Laser
Experimental Setup
Metal diatomics are produced by creating a plasma around a V metal rod, and then adding Cr(CO)6 or Mo(CO)6.
Spectra were taken with flow tube at room temperature.
52Cr51V and 92Mo51V were mass selected.
About 25 pA of CrV and 0.5 pA of MoV were produced under these conditions.
Likely Electronic States
Neutral: V 4s23d3 Cr 4s13d5 Mo 5s14d5
Anions: V 4s23d4 Cr 4s23d5 Mo 5s24d5
Excited state: V 4s13d4 2112 cm-1
Anion1d2d4d4s2 3 : d2d4d3s2s*1
Neutral2 : d2d4d3s2 4: d2d4d3s1s*1
2d2d4d4s1 4d2d4d2s2s*1
Ground State of Neutrals Known
Resonant two-photon ionization studies by Morse and co-workers have established the ground states and bond lengths of CrV and MoV.1,2
22.5 d2d4d3s2
CASSCF/CASPT2 by Andersson on CrV.3 12 electronic states were calculated.The ground state agrees with experiment.The states are multiconfigurational. The
configuration above is weighted at 57%.
1) Sickafoose, S. M.; Langenberg, J. D.; Morse, M. D. J. Phys. Chem. A 2000, 104, 3521.2) Nagarajan, R.; Sickafoose, S. M.; Morse, M. D. J. Chem. Phys. 2007, 127, 014311.3) K. Andersson. Theo. Chem. Acct. 2003, 110, 218 correct
DFT: MoV and CrV
Gaussian 03
CrV BPW91/6-311+G(df)1
MoV BPW91/SDD (Stuttgart-Dresden ECP) Various electronic states were explored. In
order to find the ground state. States relevant to the photoelectron spectra
are presented here.
1 ) Gutsev,G.L.; Mochena, M.D.; Jena, P.; Bauschlicher, C.W.; Partridge, H. J. Chem. Phys. 2004, 121, 6785.
MoV: 2.540 eV (488nm) Spectrum
0
200
400
600
800
1000
0.550.750.951.151.351.551.751.952.152.35
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
2 33
2 1+
2 1
High Binding Energy: 3 Transitions
MoV: Ground States
0
500
1000
1500
2000
2500
0.70.80.911.11.21.3
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
2 1
*=2.5
*=1.5
0-0
1-0
2-0
3-0
4-05-06-0
0-1
0-2
0-0
1-0
2-0
3-0
4-05-0
0-1
0-2
0-1
MoV: Ground States
Anion: 1d2d4d4s2 to Neutral: 2 d2d4d3s2
Detachment from dExperimental Calculated
EA 0.932 eV 0.721 eV
Δre ± 0.063 Å 0.115 Å
e Anion 578 cm-1 621 cm-1
exe Anion --------- ----------
e Neutral 508 cm-1 407 cm-1
exe Neutral 2.8 cm-1 ----------
SO2.5-1.5 645 cm-1 ----------
MoV: First Excited Neutral
0
1000
2000
3000
4000
5000
6000
7000
8000
1.251.351.451.551.651.751.851.952.052.15
Electron Binding Energy (eV)
Ph
oto
ele
ctr
on
Co
un
ts
x10
2 1
0-0
1-0
2-0
3-0
4-0
5-0
6-07-08-0
9-010-0
MoV: First Excited Neutral
Anion: 1d2d4d4s2 to Neutral: 2d2d4d4s1
Detachment from sExperimental Calculated
To 1.345 eV 1.307 eV
Δre ±0.053 Å -0.019 Å
e Anion 572 cm-1 407 cm-1
exe Anion --------- ----------
e Neutral 651 cm-1 533 cm-1
exe Neutral 3.7 cm-1 ----------
MoV: Excited Anion State
0
100
200
300
400
500
0.550.60.650.70.750.8
Electron Binding Energy (eV)
Ph
oto
ele
ctr
on
Co
un
ts
2 33
0-0
0-0
0-1
0-0
1-0
2-0
1-0
0-0
MoV: Excited Anion State
Anion: 3d2d4d3s2s*1 to Neutral:2d2d4d3s2
Detachment from s*Experimental Calculated
T0 0.284 eV 0.130 eV
Δre ± 0.040 Å -0.012 Å
e Anion --------- 393 cm-1
exe Anion --------- ----------SO 3-2 160 cm-1 ----------
e Neutral 508 cm-1 406 cm-1
exe Neutral 2.8 cm-1 ----------
CrV: 514.5nm (2.409 eV) Spectrum*
0
5000
10000
15000
20000
25000
0.40.60.811.21.41.61.822.2
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
2 33
2 33
4 33
High Binding Energy: 3 Transitions
Spectra reproduced from Ph.D. thesis by Simson Alex 1997
CrV: Ground State (2.409 eV)
0
5000
10000
15000
20000
25000
0.40.50.60.70.80.911.1
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
x10x10
0-0
1-02-0
3-0
4-05-06-07-08-09-0
0-1
2 33
CrV: Ground State Spin-Orbit
0
5000
10000
15000
20000
25000
0.480.490.50.510.520.530.540.550.56
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
2 33
0-0
CrV: Ground State
Anion: 3d2d4d3s2s*1 to Neutral: 2d2d4d3s2
Detachment from s*
Experimental Calculated*
EA 0.521 eV 0.492 eV
Δre ± 0.03 Å -0.001 Å
e Anion 409 cm-1 491 cm-1
exe Anion -------- ----------
e Neutral 520 cm-1 499 cm-1
exe Neutral 7.2 cm-1 ----------*DFT finds the 1 to be the anionic ground state; the 3 is 0.15 eV above it.
CrV: First Excited Neutral (2.409 eV)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
11.11.21.31.41.51.6
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
x5
2 33 0-0
1-0
2-03-0
4-0
5-0
6-0
********
??
CrV: First Excited Neutral
Anion:3d2d4d3s2s*1 to Neutral: 2d2d4d4s1
Two electron process
Experimental Calculated
To 0.556 eV 0.301 eV
Δre ± 0.05 Å 0.123 Å
e Neutral 715 cm-1 875 cm-1
exe Neutral 12.3 cm-1 ----------
e Anion 409 cm-1 491 cm-1
Summary
The ground electron state of the anions, MoV and CrV, were found to be different.
MoV- 1+ vs. CrV- 3
The force constants for the states are large.
1d2d4d4s2 2d2d4d4s1
MoV- 1+ 6.45 Cr2 1g
3.541
MoV 28.19 Mo2 1g+ 6.331
CrV 2 7.75 Cu2 1g
+ 1.331
Units are mdyne/Å1) Lombardi, J. R.; Davis, B. Chem. Rev. 2002, 102, 2431.
Thanks
Doreen Leopold advisor Simson Alex for CrV experimental data Minnesota Supercomputing Institute Research Corporation
CrV: Ground State Spin-Orbit
The uneven spin-orbit spacing in the anion 3 implies the existence of a low lying excited state; not seen in the spectrum.
State Spacing Neutral2.5-1.5 270 cm-1
Anion 3-2 70 cm-1
Anion 2-1 335 cm-1
Spin-Orbit States
Can have spin-orbit transition when orbital angular momentum is not 0.
Using a simple first order approach the spin-orbit states should be evenly spaced by A.
Eso=A A is negative so highest state is lowest.
MoV CrV3 427 cm-1 210 cm-1 = 3,2,12 854 cm-1 420 cm-1 = 2.5,1.5
MoV: High Binding Energy
0
50
100
150
200
250
300
350
2.052.12.152.22.252.32.352.42.452.5
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
CrV: Second Excited Neutral (2.409 eV)
0
50
100
150
200
250
300
350
400
450
500
1.581.631.681.731.781.831.88
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts
0-04 33
1-02-0
3-0
4-0
0-1
CrV: Second Excited Neutral (2.409 eV)
Anion:3d2d4d3s2s*1 to Neutral:4d2d4d3s1s*1
Detachment from a d
Experimental Calculated
To 1.143 eV N/A
Δre 0.05 Å N/A
e Neutral 440 cm-1 N/A
exe Neutral <4.0 cm-1 N/A
e Anion 409 cm-1 491 cm-1
CrV High Binding Energy (2.601eV)
0
100
200
300
400
500
600
1.922.12.22.32.42.5
Electron Binding Energy (eV)
Ph
oto
elec
tro
n C
ou
nts4CrV*
0-0
1-02-0
3-0
433
0-0
1-02-0
3-04-0
5-0
4 330-0
1-0
2-0
0-1