Compound states of triatomic molecules and simple hydrocarbons are studied using electron transmission spectroscopy. Structures in the derivative of the current transmitted through a gas‐filled collision chamber are interpreted as resonances in the electron‐molecule cross sections. At low electron energies (0–6 eV) we observe, in N2O, H2S, and C2H4, broad and featureless structures which we identify as shape resonances. In the same energy range, the molecules CO2, NO2, C6H6, and SO2 exhibit narrow structures which form vibrational progressions. In CO2, NO2, and C6H6, these vibrational progressions are identified as shape resonances; in SO2, the interpretation is not clear cut. No low‐energy resonances are observed in H2O and in CH4. At higher energies (9–17 eV) we observe sharp structures for H2O, H2S, N2O, CO2, and C2H4 (but not for C6H6 and CH4). These structures form bands, each band consisting of a vibrational progression. The states which are responsible for the bands consist of two Rydberg electrons moving in the field of a particular positive‐ion core. These bands are similar to those found previously in diatomic molecules.
REFERENCES
1.
2.
3.
4.
5.
M. J. W.
Boness
, J. B.
Hasted
, and I. W.
Larkin
, Proc. Roy. Soc. (London)
A305
, 493
(1968
).6.
H. S.
Taylor
, Advan. Chem. Phys.
18
, 91
(1970
);see also
H. S.
Taylor
, G. V.
Nazaroff
, and A.
Golebiewski
, J. Chem. Phys.
45
, 2872
(1966
).7.
8.
H. S. W. Massey, Electronic and Ionic Impact Phenomena (Clarendon, Oxford, England, 1969), 2nd ed.
9.
A. Herzenberg, Method and Problems of Theoretical Physics, edited by J. E. Bowcock (North‐Holland, Amsterdam, 1967).
10.
11.
12.
13.
14.
15.
Such an interference occurs because the line shape of a resonance profile may be quite different in different exit channels.
16.
The larger the natural width of the resonance the greater will be the shift in a particular feature position, unless the feature is coincident in energy with the resonance center. Thus for fairly broad and partially overlapping shape resonances it is difficult to locate the center of the resonance for each vibronic state.
17.
18.
19.
D. Andrick and D. Danner (unpublished).
20.
21.
22.
G. Herzberg, Electronic Spectra and Electronic Structure of Polyatomic Molecules (Van Nostrand, Princeton, New Jersey, 1967).
23.
24.
M. Krauss (private communication).
25.
26.
D. B.
Dunkin
, F. C.
Fehsenfeld
, and E. E.
Ferguson
, Chem. Phys. Letters
15
, 257
(1972
).27.
28.
29.
30.
31.
Structures observed in transmission may sometimes be due to rapid changes in the inelastic cross section related to sharp inelastic onsets. Resonances and sharp onsets can be recognized by the shape of the structure they produce in the derivative of the transmitted current. Sharp onsets produce dips in the derivative curve whereas a resonance produces at least one maximum and one minimum in the derivative curve [e.g., see
L.
Sanche
and G. J.
Schulz
, Phys. Rev. Letters
26
, 943
(1971
)]. Thus the shape of the derivative transmission profile seen in Fig. 4 indicates that the structure is due to the presence of a temporary negativeion state. This is further verified by noting that the first excited state of lies at 3.42 eV (i.e., 0.55 eV above the zeroth level of the lower band).32.
R. A. Bennett and R. J. Celotta (unpublished);
K.
Krauss
, W.
Müller‐Dunsing
, and H.
Neuert
, Z. Naturforsch.
16a
, 1385
(1961
);D.
Feldmann
, Z. Naturforsch.
25a
, 621
(1970
).33.
34.
M. Krauss (private communication).
35.
36.
37.
38.
39.
40.
41.
J. N. Bardsley, A. Herzenberg, and F. Mandl, Atomic Collision Processes, edited by M. R. C. McDowell (North‐Holland, Amsterdam, 1964), p. 415.
42.
The use of this expression to estimate the average autoionization width is also discussed by
M. J. W.
Boness
and G. J.
Schulz
, Phys. Rev. Letters
21
, 1031
(1968
).43.
44.
F. Fiquet‐Fayard (private communication).
45.
J. L. Mauer and G. J. Schulz, Phys. Rev. A (to be published).
46.
F.
Fiquet‐Fayard
, J. P.
Ziesel
, R.
Azria
, M.
Tronc
, and J.
Chiari
, J. Chem. Phys.
56
, 2540
(1972
).47.
Although both processes probably arise from the same state they need not be coincident in energy. The 2.2 eV peak in the cross section for production can be slightly displaced from the resonance center since the magnitude of the cross section depends exponentially on the natural width of the resonance and the stabilization time.
48.
M. J. W.
Boness
, I. W.
Larkin
, J. B.
Hasted
, and L.
Moore
, Chem. Phys. Letters
1
, 292
(1967
).49.
50.
H.‐J.
Hubin‐Franskin
and J. E.
Collin
, Int. J. Mass. Spectrom. Ion. Phys.
5
, 163
(1970
);see also
H. H.
Brongersma
, A. J. H.
Boerboom
, and J.
Kistemaker
, Physica
44
, 449
(1969
).51.
52.
Von L. v.
Trepka
and H.
Neuert
, Z. Naturforsch.
18a
, 1295
(1963
).53.
R. N.
Compton
, L. G.
Christophorou
, and R. H.
Huebner
, Phys. Letters
23
, 656
(1966
);See also
R. N.
Compton
, R. H.
Huebner
, P. W.
Reinhardt
, and L. G.
Christophorou
, J. Chem. Phys.
48
, 901
(1968
).54.
E. N.
Lassettre
, A.
Skerbele
, M. A.
Dillon
, and K. J.
Ross
, J. Chem. Phys.
48
, 5066
(1968
).55.
P. D. Burrow and L. Sanche (private communication). The experimental arrangement for observing 180° scattering is described in Ref. 20.
56.
C. E. Melton, Principles of Mass Spectrometry and Negative Ions (Dekker, New York, 1970), p. 273.
57.
C. R.
Brundle
and D. W.
Turner
, Proc. Roy. Soc. (London)
A307
, 27
(1968
).58.
A. W.
Potts
and W. C.
Price
, Proc. Roy. Soc. (London)
A326
, 181
(1972
).59.
E.
Lindholm
, Arkiv Fysik
40
, 129
(1969
).60.
61.
E.
Lindholm
, Arkiv Physik
40
, 125
(1969
).62.
The approximate energy level of an unobserved Rydberg state is deduced from the energy of an optically allowed Rydberg state which has the same electron orbital configuration but which has a different ion core.
63.
64.
A. D.
Baker
, C.
Baker
, C. R.
Brundle
, and D. W.
Turner
, Intern. J. Mass Spectroy. Ion Phys.
1
, 285
(1968
).65.
This content is only available via PDF.
© 1973 The American Institute of Physics.
1973
The American Institute of Physics
You do not currently have access to this content.