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Photoelectron Photoion Coincidence Spectroscopy:
Trimethylphosphine
András Bődi
Málstofa í efnafræðiRaunvísindastofnun 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
http://www.chem.unc.edu/people/faculty/baert/tbgroup/PEPICO_Home_Page.htmlhttp://www.chem.elte.hu/departments/altkem/sztaray/
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
Dissociative Photoionization
• Neutral thermal energy distribution
• h→ photoionization• Dissociation• Consecutive and parallel
recations– k, k1, k2
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–
Detection of Zero Kinetic Energy Electrons
• Threshold Photoelectron Photoion Coincidence
• Energetics
h = IEad + Eintion + KEion + KEe
Conservation of momentum
Detection of zero kinetic E e–
Apparatus I
Tunable h source (H2 lamp)
Grating monochromator
Sample chamber
Reflectron
e– optics
Sample inlet
P(CH3)3 Data – TOF Distributions
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96Ion time-of-flight / ms
PE
PIC
O s
igna
l / a
rb. u
nits
10.76 eV
10.87 eV
11.09 eV
12.07 eV
P(CH3)3 Data – Breakdown Curves
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10.5 10.7 10.9 11.1 11.3 11.5 11.7 11.9 12.1 12.3 12.5 12.7
Photon energy / eV
Rel
ativ
e ab
unda
nce
H2CP(CH3)2+
H2CPCH3+
HP(CH2)(CH3)+
P(CH3)3+
Simulation Overview
P(CH3)3+ freq. & rot.
const.
P(CH3)3 vibrational frequencies & rotational constants
Ion optics parameters
P(CH3)3 internal energy distribution
IEad
P(CH3)3+
internal energy distribution
RRKM + TOF calculation
varie
d to
acq
uire
the
best fi
t
Transition state frequenciesBond energiesTunneling params.
Ab initio input
Ab initio Input: Bond Energies
E0 / (kJ/mol)P(CH3)3
+ CCSD(T)/ cc-pVTZ G3 Expt.
P(CH3)2+ + CH3 304 308 242.3
HP(CH2)CH3+ + CH3
269 267 242.3 P(CH2)(CH3)2
+ + H 252 248 241.6 P(CH2)CH3
+ + CH4 239 249 155 – 250 TS (CH3)2P
…H…CH2+ 199 –
HP(CH2)(CH3)2+ 40 34
Potential Energy Curves
E
(a)
(TSab) (CH3)2P…H…CH2+ (c) HP(CH2)CH3
+ + CH3
(e) P(CH2)CH3+ + CH4
P(CH3)3+
P(CH3)2+ + CH3
(d) P(CH2)(CH3)2+ + H
(d) P(CH2)(CH3)2+ + H
(b) HP(CH2)(CH3)2+
(TSbe) (H2C)(H3C)P…H…CH3+
Gas Phase ThermochemistryΔ
fH°
P(CH3)3
P(CH3)3+
P(CH2)(CH3)+
P(CH2)(CH3)2+ HP(CH2)(CH3)+
IE
AE3 AE2
AE1
Analogous Parent
IE + AEn
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
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