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.html http://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(CH 3 ) 3 Data analysis and modeling Ab initio calculations Thermochemistry

4. Dissociative Photoionization Neutral thermal energy distribution h  → photoionization Dissociation Consecutive and parallel recations –k, k 1, k 2 h dissociation AB A + B 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 h e – optics Ion optics

7. Detection of Zero Kinetic Energy Electrons Threshold Photoelectron Photoion Coincidence Energetics h = IE ad + E int ion + KE ion + KE e Conservation of momentum Detection of zero kinetic E e –

8. Apparatus I Tunable h source (H 2 lamp) Grating monochromator Sample chamber Reflectron e – optics Sample inlet

9. Apparatus II h e–e– ion

10. P(CH 3 ) 3 – Photodissociation Products ? CH 3 loss CH 4 loss H loss

11. P(CH 3 ) 3 Data – TOF Distributions

12. P(CH 3 ) 3 Data – Breakdown Curves

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

14. Ab initio Input: Bond Energies

15. Potential Energy Curves E (a) (TS ab ) (CH 3 ) 2 P … H … CH 2 + (c) HP(CH 2 )CH 3 + + CH 3 (e) P(CH 2 )CH 3 + + CH 4 P(CH 3 ) 3 + P(CH 3 ) 2 + + CH 3 (d) P(CH 2 )(CH 3 ) 2 + + H (b) HP(CH 2 )(CH 3 ) 2 + (TS be ) (H 2 C)(H 3 C)P … H … CH 3 +

16. Gas Phase Thermochemistry ΔfH°ΔfH° P(CH 3 ) 3 P(CH 3 ) 3 + P(CH 2 )(CH 3 ) + P(CH 2 )(CH 3 ) 2 + HP(CH 2 )(CH 3 ) + IE AE 3 AE 2 AE 1 Analogous Parent IE + AE n

17. Recapitulation TPEPICO – Photoionization followed by the detection of photoions and zero kinetic energy photoelectrons in coincidence Measurement – TOF spectra vs h 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.