Threshold photoelectrons

Similar values have been obtained for AHffMesSi ) from two independent studies. The bond dissociation enthalpy DHfMeaSi-SiMea) = 332 +12 kJ moC was obtained from a kinetic study on the very low pressure pyrolysis of hexamethyldisilane and the enthalpy of formation of trimethylsilyl ion, AHf (MeaSi ) = 617.3 + 2.3kJmor, was determined using threshold photoelectron-photoion coincidence spectroscopy (TPEPICO). Both data are related to AHf°(Me3Si ). 

B. Zero Kinetic Energy Threshold Photoelectron Spectroscopy and... 

Miiller-Dethlefs, K. Sander, M. Schlag, E.W. A Novel Method Capable of Resolving Rotational Ionic States by the Detection of Threshold Photoelectrons with a Resolution of 1.2 cm". Z. Naturforsch. 1984,59a, 1089-1091. 

Davalos, J. Z. Baer, T. Thermochemistry and Dissociative Photoionization of Si(CH3)4, BrSifCITjlj, ISifCEIjlj, and SijCCElj) Studied by Threshold Photoelectron-Photoion Coincidence Spectroscopy/. Phys. Chem. A 2006, 110, 8572-8579. 

A number of techniques have been used previously for the study of state-selected ion-molecule reactions. In particular, the use of resonance-enhanced multiphoton ionization (REMPI) [21] and threshold photoelectron photoion coincidence (TPEPICO) [22] has allowed the detailed study of effects of vibrational state selection of ions on reaction cross sections. Neither of these methods, however, are intrinsically capable of complete selection of the rotational states of the molecular ions. The TPEPICO technique or related methods do not have sufficient electron energy resolution to achieve this, while REMPI methods are dependent on the selection rules for angular momentum transfer when a well-selected intermediate rotational state is ionized in the most favorable cases only a partial selection of a few ionic rotational states is achieved [23], There can also be problems in REMPI state-selective experiments with vibrational contamination, because the vibrational selectivity is dependent on a combination of energetic restrictions and Franck-Condon factors. 

Fig. 11.19 Cross sections for Rydberg electron, Rb nd ( ), Rb ns (x) (ref. 84), Xe nf ( ) (ref. 85), and free-electron (A) (ref. 88) attachment to SF6. The solid lines show the theoretical result of Klots (ref. 86) and the results of threshold photoelectron spectroscopy by electron attachment(TPSA) studies (ref. 87) (from ref. 84).

TPEPICO threshold photoelectron-photoion coincidence TPES threshold photoelectron spectroscopy... 

The threshold photoelectron-photoion coincidence technique using synchrotron radiation has been employed to study state-selected ion-molecule reactions. We review the experimental procedure and discuss our results on five representative systems [N2Ar]+ [N2H2]+ [ArH2]+ [HeH2]+ and [H2HJ+. Recent theoretical work on these systems is also summarized. 

The study of ion-molecule reactions using state-selected reagents has become a very exciting area of molecular dynamics. We have developed an experimental apparatus in Orsay which utilizes the properties of our tunable synchrotron radiation source at LURE to prepare ions in selected vibronic levels and then to study their reactions. The ions are state-selected using the TPEPICO (threshold-photoelectron/photoion coincidence) method [1]. 

Fig. 2. Threshold photoelectron spectrum of N2 [2] obtained under the experimental conditions described in the text. The count rate for the N2 (X, v = 1) peak was 2000 counts/sec. It is possible to increase the resolution and cleanly separate peaks for N2+ (X, v = 4) and N2 (A, v = 0) [9]...

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