Photoelectron Photoion Coincidence Spectroscopy: Trimethylphosphine

1. Photoelectron Photoion Coincidence Spectroscopy:Trimethylphosphine András Bődi Málstofa í efnafræði Raunvísindastofnun Háskólans Reykjavík, 18/02/2005

2. Acknowledgements • Baer Group, University of North Carolina • Tomas Baer, Jim Kercher • Photoelectron Spectroscopy Group,Eötvös University, Búdapest • Bálint Sztáray, Zsolt Gengeliczki, László Szepes http://www.chem.unc.edu/people/faculty/baert/tbgroup/PEPICO_Home_Page.htmlhttp://www.chem.elte.hu/departments/altkem/sztaray/

3. Outline • Introduction to TPEPICO • Why detect photoelectron and photoions? • Why the coincidence? • Experimental setup • The measurement of P(CH3)3 • Data analysis and modeling • Ab initio calculations • Thermochemistry

4. dissociation hn Dissociative Photoionization • Neutral thermal energy distribution • hn → photoionization • Dissociation • Consecutive and parallel recations • k, k1, k2 A+ + B AB+ A + B AB

5. Photoelectrons and Photoions • Photoionization Mass Spectrometry • M + hν M+ + e– • Information: dissociation of the ion • Ultraviolet Photoelectron Spectroscopy • M + hν M+ + e– • Information: ionization energies (MO energies) • Photoelectron Photoion Coincidence Spectroscopy • M + hν M+ + e–

6. Coincidence • Start signal – e– • Stop signal – ion Mass Spectrum at hn e– optics Ion optics

7. Detection of zero kinetic E e– Conservation of momentum Detection of Zero Kinetic Energy Electrons • Threshold Photoelectron Photoion Coincidence • Energetics hn = IEad + Eintion + KEion + KEe

8. Apparatus I Grating monochromator Sample inlet Reflectron e– optics Tunable hn source (H2 lamp) Sample chamber

9. Apparatus II hn ion e–

10. P(CH3)3 –Photodissociation Products ? CH3 loss CH4 loss H loss

11. P(CH3)3 Data –TOF Distributions

12. P(CH3)3 Data –Breakdown Curves

13. Simulation Overview P(CH3)3 vibrational frequencies & rotational constants P(CH3)3 internal energy distribution P(CH3)3+ freq. & rot. const. IEad Ab initio input P(CH3)3+ internal energy distribution Transition state frequencies varied to acquire the best fit Ion optics parameters Bond energies RRKM + TOF calculation Tunneling params.

14. Ab initio Input: Bond Energies

15. (TSbe) (H2C)(H3C)P…H…CH3+ P(CH3)2+ + CH3 (TSab) (CH3)2P…H…CH2+ (c) HP(CH2)CH3+ + CH3 (d) P(CH2)(CH3)2+ + H (d) P(CH2)(CH3)2+ + H (e) P(CH2)CH3+ + CH4 P(CH3)3+ (b) HP(CH2)(CH3)2+ (a) Potential Energy Curves E

16. ΔfH° P(CH2)(CH3)+ HP(CH2)(CH3)+ P(CH2)(CH3)2+ AE3 AE2 IE + AEn AE1 P(CH3)3+ IE P(CH3)3 Analogous Parent Gas Phase Thermochemistry

17. Recapitulation • TPEPICO – Photoionization followed by the detection of photoions and zero kinetic energy photoelectrons in coincidence • Measurement – TOF spectra vs hn • Known ion internal energy – Kinetics model for photodissociation with ab initio input • Bond energies from kinetics model – Thermochemical cycles Heats of formation

18. End Takk fyrir komuna.