Transcript MI06Beau.ppt

The Negative Ion
Photoelectron Spectra
of
MoV and CrV
Presented
by
Beau 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 ss bonding.
NPES Basics: Electron Kinetic Energy (eKE)
Electron Binding Energy (eBE)
Experiments involve the use of the photoelectric effect:
-
M + h
M +
e
The eKE is measured and the eBE found from the
difference in energy between the eKE and the photon:
h  eKE = eBE
eBE is equal to the difference in energy between the anion
and neutral states:
eBE = EElec + EVib + ERot
NPES Basics : Selection Rules
 Electronic State Transitions:
S  ±1
For example: If anion is a doublet the neutral could be
either a singlet or triplet.
Vibrational Transitions:

ion(q'')|neut (q')>|2
Intensities of vibrational transitions are governed by
Franck-Condon overlap between the anion and
neutral species.
NPES Basics : Information from
Spectra
Electron 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
 Anion
1S+: ds2dp4dd4ss2 3 : ds2dp4dd3ss2ss*1
 Neutral
2 : ds2dp4dd3ss2 4 : ds2dp4dd3ss1ss*1
2S+ : ds2dp4dd4ss1 4S: ds2dp4dd2ss2ss*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
2
2
4
3
2
2.5 ds dp dd ss
 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
2 S +  1S +
1000
600
400
2
High Binding Energy: 3 Transitions
2.5 
1S +
2
2.5 
200
3
3
0
2.35
2.15
1.95
1.75
1.55
1.35
1.15
Electron Binding Energy (eV)
0.95
0.75
0.55
Photoelectron Counts
800
MoV: Ground States
1S+

2.5
*=W 2.5
2000
*=W 1.5
1-0
1-0
1500
0-0
2-0
2-0
3-0
0-1 4-0
5-06-0
5-0
1000
3-0
0-1
4-0
500
0-1
0-2
0-2
0
1.3
1.2
1.1
1
Electron Binding Energy (eV)
0.9
0.8
0.7
Photoelectron Counts
2
2500
0-0
MoV: Ground States
 Anion: 1S+ ds2dp4dd4ss2 to Neutral: 2 ds2dp4dd3ss2
 Detachment from dd.
Experimental
EA
0.932 eV
Δre
± 0.063 Å
we Anion
578 cm-1
wexe Anion
--------we Neutral
508 cm-1
wexe Neutral 2.8 cm-1
SO 2.5-1.5 645 cm-1
Calculated
0.721 eV
0.115 Å
621 cm-1
---------407 cm-1
-------------------
MoV: First Excited Neutral
0-0
2S+  1S+
1-0
8000
7000
4-0
10-0
8-0
7-0
4000
2-0
x10
5-0
9-0
5000
3000
6-0
2000
3-0
1000
0
2.15
2.05
1.95
1.85
1.75
1.65
1.55
Electron Binding Energy (eV)
1.45
1.35
1.25
Photoelectron Counts
6000
MoV: First Excited Neutral
 Anion: 1S+ ds2dp4dd4ss2 to Neutral: 2S+ ds2dp4dd4ss1
 Detachment from ss.
Experimental
To
1.345 eV
Δre
±0.053 Å
we Anion
572 cm-1
wexe Anion
--------we Neutral
651 cm-1
wexe Neutral 3.7 cm-1
Calculated
1.307 eV
-0.019 Å
407 cm-1
---------533 cm-1
----------
MoV: Excited Anion State
3

2.5
3
0-0
W2.5  W3
500
400
0-0
W2.5  W2
300
1-0
W2.5  W3
0-0
0-0
W1.5  W1
W1.5  W2
0.8
0-1
1-0
2-0
W2.5  W3
W2.5  W2
0.75
0.7
200
0.65
Electron Binding Energy (eV)
0.6
100
0
0.55
Photoelectron Counts
2
MoV: Excited Anion State
 Anion: 3 ds2dp4dd3ss2ss*1 to Neutral:2 ds2dp4dd3ss2
 Detachment from ss*
Experimental
T0
0.284 eV
Δre
± 0.040 Å
we Anion
--------wexe Anion
--------SO W3-W2 160 cm-1
we Neutral 508 cm-1
wexe Neutral 2.8 cm-1
Calculated
0.130 eV
-0.012 Å
393 cm-1
------------------406 cm-1
----------
CrV: 514.5nm (2.409 eV) Spectrum*
Spectra reproduced from Ph.D. thesis by Simson Alex 1997
2
2.5 
3
25000
3
15000
10000
2S +  3
High Binding Energy: 3 Transitions
4
2.2
2
1.8
3.5
+  3
1.6
5000
3
3
0
1.4
1.2
Electron Binding Energy (eV)
1
0.8
0.6
0.4
Photoelectron Counts
20000
CrV: Ground State (2.409 eV)
2
25000
0-0
3

2.5
3
0-1
15000
3-0
10000
9-0
8-0
7-0
6-0
5-0
x10
4-0
x10
2-0
5000
1-0
0
1.1
1
0.9
0.8
0.7
Electron Binding Energy (eV)
0.6
0.5
0.4
Photoelectron Counts
20000
CrV: Ground State Spin-Orbit
2
W2.5  W3
3

2.5
3
0-0
25000
W2.5  W2
15000
10000
W1.5  W1
5000
W1.5  W2
0
0.56
0.55
0.54
0.53
0.52
0.51
Electron Binding Energy (eV)
0.5
0.49
0.48
Photoelectron Counts
20000
CrV: Ground State
 Anion: 3 ds2dp4dd3ss2ss*1 to Neutral: 2 ds2dp4dd3ss2
 Detachment from ss*
Experimental
EA
0.521 eV
Δre
± 0.03 Å
we Anion
409 cm-1
wexe Anion
-------we Neutral
520 cm-1
wexe Neutral 7.2 cm-1
*DFT
Calculated*
0.492 eV
-0.001 Å
491 cm-1
---------499 cm-1
----------
finds the 1S+ to be the anionic ground state; the 3 is 0.15 eV above it.
CrV: First Excited Neutral (2.409 eV)
4500
3
0-0
4000
3500
4-0
3000
5-0
x5
6-0
?
2500
?
2000
1-0
1500
2-0
3-0
*
*
1000
*
*
*
*
*
*
500
0
1.6
1.5
1.4
1.3
Electron Binding Energy (eV)
1.2
1.1
1
Photoelectron Counts
2S +  3
CrV: First Excited Neutral
 Anion:3 ds2dp4dd3ss2ss*1 to Neutral: 2S+ ds2dp4dd4ss1
 Two electron process
Experimental
To
0.556 eV
Δre
± 0.05 Å
we Neutral 715 cm-1
wexe Neutral 12.3 cm-1
we Anion
409 cm-1
Calculated
0.301 eV
0.123 Å
875 cm-1
---------491 cm-1
Summary
 The ground electron state of the anions, MoV and
CrV, were found to be different.
MoV- 1S+ vs. CrV- 33
 The force constants for the S states are large.
1S+: ds2dp4dd4ss2
2S+: ds2dp4dd4ss1
MoV- 1S+ 6.45
MoV 2S+ 8.19
CrV 2S+ 7.75
Units are mdyne/Å
1) Lombardi, J. R.; Davis, B. Chem. Rev. 2002, 102, 2431.
Cr2 1Sg+ 3.541
Mo2 1Sg+ 6.331
Cu2 1Sg+ 1.331
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
Neutral W2.5-W1.5
Anion W3-W2
Anion W2-W1
270 cm-1
70 cm-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 spinorbit states should be evenly spaced by A.
Eso=ALS
 A is negative so highest W state is lowest.
MoV
CrV
3
-1
-1 W= 3,2,1
427
cm
210
cm
3
2
-1
-1 W= 2.5,1.5
854
cm
420
cm
2.5
MoV: High Binding Energy
350
300
200
150
100
50
2.5
2.45
2.4
2.35
2.3
2.25
Electron Binding Energy (eV)
2.2
2.15
2.1
0
2.05
Photoelectron Counts
250
CrV: Second Excited Neutral (2.409 eV)
3

3.5
3
0-0
450
400
2-0
0-1
1-0
350
300
250
3-0
200
4-0
150
100
50
0
1.88
1.83
1.78
1.73
Electron Binding Energy (eV)
1.68
1.63
1.58
Photoelectron Counts
4
500
CrV: Second Excited Neutral (2.409 eV)
 Anion:3 ds2dp4dd3ss2ss*1 to Neutral:4 ds2dp4dd3ss1ss*1
 Detachment from a ds.
Experimental
To
1.143 eV
Δre
0.05 Å
we Neutral 440 cm-1
wexe Neutral <4.0 cm-1
we Anion
409 cm-1
Calculated
N/A
N/A
N/A
N/A
491 cm-1
CrV High Binding Energy (2.601eV)
4
600
0-0
500
1-0
2-0
3-0
4-0
400
1-0
3-0 2-0
300
2-0
1-0
200
0-0
5-0
0-0 0-1
100
0
2.5
2.4
2.3
2.2
Electron Binding Energy (eV)
2.1
2
1.9
Photoelectron Counts
3

3.5
3
4 S   3
3
4 CrV*
3.5