1. Vibrational Predissociation Spectroscopy of Metal Carbonyl Complexes 1: Co(CO)n+ (n=1-10)
Allen M. Ricks and Michael A. Duncan
Department of Chemistry
University of Georgia, Athens Ga.
*(2 will be on Thursday RA08)

2. Fe(CO)5, Co(CO)5+ and the 18-electron rule
Iron pentacarbonyl, Fe(CO)5 is a known stable compound
Fe is d6 so Fe(CO)5 satisfies the 18-electron rule
Has a known D3h structure
So popular it even has its own wikipedia page
Co+ is isoelectronic to Fe
Presumably Co(CO)5+ would have the same structure as Fe(CO)5

3. Mass selection of cations by time-of-flight.
full mass spectrum
activate mass gate;
select one cluster mass.
excite at turning point.
Production of cold cations and complexes with laser vaporization in a supersonic expansion.
Mass selection of cations by time-of-flight.
Tunable laser photodissociation with IR OPO; measure fragment intensity versus wavelength.
photofragments
parent ion depletion

4. Tunable IR Spectroscopy
LaserVision Tunable Infrared Laser System
designed by Dean Guyer
Tuning range: cm-1 Linewidth: ~1.0 cm-1
cm-1
Tunable mid-IR m
cm-1
Tunable m
OPO
OPA
idler
KTP
oscillator
KTA
diff. gen.
+ amp of idler beam
AgGaSe2
diff. gen.
532 nm
signal
(not used)
1 crystal
angle tuned
4 crystals
angle tuned
1 crystal
angle tuned
1064 nm
Pumped by pulsed, unseeded YAG
e.g., Spectra Physics PRO-230.

5. Typical Mass spectrum observed in this experiment
Addition of water is necessary to facilitate ion formation
The peak corresponding to Co(CO)5+ is dominant over other cluster sizes
Indicates inherent stability of this complex
This is the 18-electron species

6. Infrared photofragmentation breakdown spectra
Infrared photodissociation breakdown spectra show termination at n=5, again indicating the stability of this complex
We were able to fragment the n=5 complex, however it is inefficient and we believe it to due to multiphoton absorption

7. Infrared Spectra of Co(CO)n+ (n=5-9) measured via elimination of CO
Dashed line shows νco stretch at 2143 cm-1
The band at ~2166 cm-1 is due to “surface” carbonyls, those beyond the coordination sphere
This corresponds to a 23 cm-1 shift to the blue from the gas phase CO value
Is due to the electrostatic interaction of the carbonyls with the core ion
Bands at ~2140 and ~2150 assigned to Co(CO)5+ core ion
Spectrum of n=5 featureless, supporting our assumption that fragmentation of this complex is caused by multiphoton absorption

8. Infrared spectra of Co(CO)n+ complexes obtained via rare gas tagging
Spectrum of Co(CO)5+ obtained via rare gas tagging shows structure not observed in previous spectrum
Appears to be a 15 cm -1 frequency shift between Co(CO)4+ and Co(CO)5+
Spectrum of Co(CO)3+ shows one CO stretch consistent with a D3h structure
Single peak in Co(CO)2+ spectrum indicates a D∞h structure
Doubly argon tagging required for Co(CO)1+ due to high binding energy

9. Comparison of experimental and theoretical spectra of larger argon tagged cobalt carbonyl complexes
Theoretical calculations help us elucidate the multiplicity of the complexes being studied
There is a spin change between n=4 and n=5
Singlet Co(CO)5+ is isoelectronic to the 18-electron Fe(CO)5 complex

10. Comparison of experimental and theoretical spectra of smaller argon tagged cobalt carbonyl complexes
Spectrum of Co(CO)5+ obtained via rare gas tagging shows structure not observed in previous spectrum
Appears to be a 15 cm -1 frequency shift between Co(CO)4+ and Co(CO)5+
Spectrum of Co(CO)3+ shows one CO stretch consistent with a D3h structure
Single peak in Co(CO)2+ spectrum indicates a D∞h structure
Doubly argon tagging required for Co(CO)1+ due to high binding energy

11. Structures of small cobalt carbonyl and argon tagged cobalt carbonyl complexes
Structures of Co(CO)5+ complexes
Argon shows large structural perturbation?
Actually due to basis set superposition error
Usage of larger basis set on metal ion alleviates this problem

12. Current work in other systems
Current work on vanadium carbonyl complexes
Have achieved efficient Ne tagging!
Spectrum of the dimer shows two peaks when neon and argon tagging
Must be due to different spin states present

13. Acknowledgements USAFRF and DOE for funding Prof. Michael Duncan
Prof. Peter Armentrout