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

Acknowledgements Baer Group, University of North Carolina –Tomas Baer, Jim Kercher Photoelectron Spectroscopy Group, Eötvös University, Búdapest –Bálint Sztáray, Zsolt Gengeliczki, László Szepes

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

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 +

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 –

Coincidence Start signal – e – Stop signal – ion Mass Spectrum at h e – optics Ion optics

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 –

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

Apparatus II h e–e– ion

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

P(CH 3 ) 3 Data – TOF Distributions

P(CH 3 ) 3 Data – Breakdown Curves

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

Ab initio Input: Bond Energies

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

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

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

End Takk fyrir komuna.