Supplementary material
We present here the details of the experimental observation of the diatomic dication IO2+ in
the gas phase by Franzreb and Williams in 2008. These authors used mass spectrometry to detect the
species formed after prolonged oxygen ion beam sputtering of cesium iodide powder [Klaus Franzreb
and Peter Williams, experimental results, 2008, Arizona State University, unpublished]. Their
experimental results on gas-phase IO2+ have been briefly mentioned (data not shown) in ref. [T. V.
Alves, W. Hermoso, K. Franzreb, and F. R. Ornellas, Phys. Chem. Chem. Phys. 13, 18297 (2011).]
as well as in the supplementary material of ref. [V. Brites, K. Franzreb, J.N. Harvey, S.G. Sayres,
M.W. Ross, D.E. Blumling, A.W. Castleman. Jr, and M. Hochlaf, Phys. Chem. Chem. Phys. 13, 15233
(2011).] (please see the web link: http://www.rsc.org/suppdata/cp/c1/c1cp21566c/c1cp21566c.pdf).
Figure S1:
Two positive ion mass spectra obtained for oxygen ion beam sputtering of cesium
iodide (CsI) powder (pressed into soft indium metal foil) with a mass-filtered 420 nA,
17 keV 16O- ion beam and a square raster of 250 µm. The data shown is provided from
courtesy of Klaus Franzreb and Peter Williams at Arizona State University
(unpublished, 2008). It was acquired on a Cameca IMS 3f magnetic-sector mass
spectrometer with a count time of 2s per data point and a sample voltage of +4500V.
The novel diatomic dication IO2+ is detected at half-integer m/z 71.45 (assigned to
127 16
I O2+) with an ion intensity of about 20 c/s (single ion counts per second) and
displayed both on a semi-logarithmic and a linear intensity scale (see text for further
details).
Figure S1 shows the mass spectra acquired by Franzreb and Williams at Arizona State
University for prolonged 17 keV 16O- ion surface bombardment of cesium iodide powder pressed into
indium foil. Oxygen sputtering is used for two purposes, (i) to oxidize, i.e. incorporate oxygen ( 16O) in
the near-surface region of the cesium iodide powder, and (ii) to eject various species from the surface
into the gas phase [J. Fiser, K. Franzreb, J. Lorincik, and P. Williams, Eur. J. Mass Spectrom. 15, 315
(2009).]. Figure S1 displays two mass spectra, with the second one (open symbols) plotted offset by
the multiplication factor x500 in the semi-logarithmic presentation and by having added +40 c/s in the
linear presentation. The novel gas-phase molecular species IO2+ is observed at half-integer m/z 71.45
(assigned to
127 16
I O2+). A different assignment to an atomic (elemental) species, i.e. to
143
Nd2+, has
been ruled out because of the non-observation of a slightly less intense ion peak, i.e. there is no
145
Nd2+, at half-integer m/z 72.45.
Note that CsO2+ could not be observed in Figure S1 at half-integer m/z 74.45. We are not
aware of any experimental or theoretical information on CsO2+ in the literature, but it should be
mentioned that the alkali-oxygen dication system KO2+ had been observed in the gas phase by
Accelerator Mass Spectrometry [X.-L. Zhao, M.-J. Nadeau, M. A. Garwan, L. R. Kilius, and A. E.
Litherland, Nucl. Instrum. Meth. Phys. Res. B 52 (1990) 416 (1990)].
Other doubly-charged ion signals in Figure S1 at half-integer m/z values include
63.45,
133
Cs
2+
at m/z 66.45 as well as
135
Ba
2+
at m/z 67.45 and
137
Ba
2+
127 2+
I at m/z
at m/z 68.45. The latter two
barium contamination signals are probably due to a memory effect of the mass spectrometer because
of extensive sputtering of a barium metal sample with a high-current, 8 keV
40
Ar+ ion beam in a
previous experiment by Franzreb et al. [K. Franzreb, R. Pis Diez, J. A. Alonso, J. Chem. Phys. 130,
144312 (2009).] in an unsuccessful search for the novel diatomic dication Ba 22+ that had been
predicted to be a long-lived metastable gas-phase species by the calculation in ref. [S. J. Sramek, J. H.
Macek, and G. A. Gallup, Phys. Rev. A 21, 1361 (1980).]).
We thank Klaus Franzreb and Peter Williams for their permission to include their unpublished
experimental results in our theoretical work.