Diapositiva 1

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ELECTRON SPECTROSCOPY AND MASS SPECTROMETRIC
STUDY OF PENNING IONIZATION OF MOLECULES
F. Vecchiocattivi Dipartimento dIngegneria
Civile ed Ambientale Università degli Studi di
Perugia Perugia - Italy
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The Penning ionization process
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(1894-1953)
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F. M. Penning, Naturwissenschaften 15, 818 (1927)
(1894-1953)
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A M ? (AM) ? (AM) e-
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Perugia molecular beam apparatus for Penning
ionization studies
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He(21S, 23S) Ar ? He Ar(2P3/2, 2P1/2) e-
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B. Brunetti, P. Candori, S. Falcinelli, B.
Lescop, G. Liuti, F. Pirani, F. Vecchiocattivi
(2005) to be published
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He(3S) Ar ? He-Ar ? He-M e-
He(3S)
Ar
Ar
He
?
?
?
?
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P
P
S
W1/2
He Ar(2P1/2)
He Ar(2P3/2)
W3/2
W1/2
The relative population of the J1/2 and J3/2
states of the Ar product practically reflects
the ? character of the final He-Ar state.
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Ne(3P2,0) Ar ? Ne-Ar ? Ne-M e-
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B. Brunetti, P. Candori, S. Falcinelli, B.
Lescop, G. Liuti, F. Pirani, F. Vecchiocattivi
(2005) to be published
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Penning ionization occurs through the transfer of
an outer shell electron from the target particle
into the inner shell vacancy of the metastable
atom.
The process is therefore governed by the mutual
orientation of atomic orbitals.
In the case of atom-molecule systems, this also
implies a strong effect of the orientation of the
target molecule.
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Ar CH3Cl ? CH3Cl Ar e-
H.Ohoyama, H.Kawaguchi, M.Yamato, T.Kasai,
B.G.Brunetti, F.Vecchiocattivi, Chem.Phys.Lett.
313, 484 (1999). H. Ohoyama, M.Yamato, S.
Okada, T. Kasai, B. G. Brunetti, F.
Vecchiocattivi, Phys.Chem.Chem.Phys. 3, 3598
(2001). B. G. Brunetti, P. Candori, S.
Falcinelli, T. Kasai, H. Ohoyama, F.
Vecchiocattivi, Phys.Chem.Chem.Phys. 3, 807
(2001). V. Aquilanti, F. Pirani, D.
Cappelletti, F. Vecchiocattivi, T. Kasai, in
Theory of chemical reaction dynamics, Kluwer
Academic, the Netherlands, p.243
(2004). V.Aquilanti, M. Bartolomei, F. Pirani,
D. Cappelletti, F. Vecchiocattivi, Y. Shimizu, T.
Kasai. Phys.Chem.Chem.Phys. 7, 291 (2005)
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stereo-opacity
1.2
0.8
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Rg He, Ne
Rg N2O ? RgN2O e-
RgN2O ? N2O
? NO N
? O N2
? RgN2O
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Molecular orbitals of N2O
HOMO
LUMO
Nitrogen lone pair
Oxygen lone pair
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He(21S) N2O
He NNO
NNO He
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B. Brunetti, P. Candori, S. Falcinelli, B.
Lescop, G. Liuti, D. Malfatti, F. Pirani, F.
Vecchiocattivi (2005) to be published
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1b1 (2p? non bonding orbital)
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Ne H2O

A (2A1)

X (2B1)
Photoionization electron spectrum, energy scaled
B. Brunetti, P. Candori, S. Falcinelli, B.
Lescop, G. Liuti, D. Malfatti, F. Pirani, F.
Vecchiocattivi (2005) to be published
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Ne H2O
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The Penning ionization of molecules strongly
depends on the orientation of the molecule with
respect to the approach direction of the
metastable atom.
The orientation not only affects the ionization
probability, but also the specific reaction
following the ionization event (dissociation,
rearrangement, etc.)
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Optical Potential Model (H. Bethe, 1940)
The Potential is assumed to be complex W(R)
V(R) i/2 ?(R)
and therefore the phase shift is also
complex ???? i ??
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Differential Cross Section
Integral Cross Section
Total Ionization Cross Section
B. Brunetti, F. Vecchiocattivi, Current Topic on
Ion Chemistry and Physics, edited by C.Y. Ng, T.
Baer, I. Powis (John Wiley Sons Ltd, New York,
1993), p. 359
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J. Chem. Phys. 95, 1801 (1991)
Differential elastic cross section
Total ionization cross section
Integral scattering cross section
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Dipartimento dIngegneria Civile ed
Ambientale F. Biondini P. Candori S.
Falcinelli G. Liuti D.Malfatti
Dipartimento di Chimica V. Aquilanti B.
Brunetti F. de Angelis F. Pirani F. Tarantelli