Supplemental information for
Formation of ionic complexes in cryogenic matrices: a case study using co-deposition of Cu- with
rare gas cations in solid argon
Ryan M. Ludwig,1 David T. Moore1,a)
1
a)
Chemistry Department, Lehigh University, Bethlehem, PA 18015, USA
Author to whom correspondence should be addressed. Email address: david.moore@lehigh.edu
Includes:
Figures S1-S7
Table SI
Description of minor spectral differences for 10 K vs 20 K deposition
Ion abundance calculation
0.20
10
63Cu
A
Current (nA)
0.15
65Cu
0.10
B
8
6
4
0.05
2
0.00
0
56
60
64
68
72
40
50
60
m/z (amu)
70
80
90
100
m/z (amu)
FIG. S1. Mass spectra of copper anions from sputtering source: a) high-resolution b) high-throughput.
8
6
Ar+
Cu-
6
Current (nA)
4
4
2
2
0
0
-60
-40
-20
0
20
40
Bias (V)
60
80
100
-60
-40
-20
0
20
40
60
80
100
Bias (V)
FIG. S2. Ion energy distributions derived from stopping-potentials of anion and cation beams detected at
Faraday plate.
2.5
Absorbance (x10-2 O.D.)
40K
2.0
35K
1.5
30K
1.0
25K
0.5
20K
0.0
1750
1800
1850
1900
1950
2000
2050
Wavenumber (cm-1)
FIG. S3. Unprocessed data from figure 3 of main text showing low-frequency etaloning from
interference in the matrix. Using index of refraction of bulk argon (1.77 1), fringes correspond to matrix
thickness of ~60 m.
1.0
30K
Absorbance
0.8
0.6
20K
0.4
0.2
0.0
1750
1800
1850
1900
1950
2000
2050
Wavenumber (cm-1)
FIG. S4. Control experiment of Cu- deposition with no counter-ion in a 0.02% CO/Ar matrix deposited at
20K. Note that there are no signs of copper complexes upon deposition at 20K or upon annealing to 30K
showing the necessity of the counter-ion for the deposition process.
1.2
1.0
30K
Absorbance (x10-2 O.D.)
0.8
Ar+
0.6
0.4
Kr+
0.2
0.0
20K
0.8
Ar+
0.6
0.4
Kr+
0.2
0.0
1750
1800
1850
1900
1950
2000
2050
Wavenumber (cm-1)
FIG. S5. Deposition of Cu- into a 0.02% CO in argon matrix at 20K followed by 30K annealing during
two separate experiments using Kr+ and Ar+ as counter-ions as shown. Note that both counter-ions lead to
virtually the same spectrum. The same neutralization events occur in both cases upon annealing with the
exception of the larger Cu(CO)3- species persisting longer in the Kr+ case.
Absorbance (x10-2 O.D.)
0.8
0.6
Ar+
0.4
0.2
0.0
1800
Kr+
1815
1830
1845
1860
1875
Wavenumber (cm-1)
FIG. S6. Deposition of Cu- into a 0.02% CO in argon matrix at 20K during two separate experiments
using Kr+ and Ar+ as counter-ions as shown. Spectra are zoomed in on the Cu(CO)3- and [Cu(CO)3•
(CO)n]- regions to emphasize the reproducibility of fine structure contained within the broad feature.
1.6
8hr
Absorbance (x10-2 O.D.)
1.4
1.2
6hr
1.0
0.8
4hr
0.6
2hr
0.4
0hr
0.2
0.0
1750
1800
1850
1900
1950
2000
2050
Wavenumber (cm-1)
FIG. S7. Time-lapse study using sample with ~7 nA Cu- & Ar+ co-deposited in a 0.02% CO in argon
matrix at 20 K. Sample was maintained at 10K over the course of 8 hours with scans taken every two
hours. Spectra show neutralization attributed to long-range photodetachment mechanism (see Fig 5B of
main text).
Description of minor spectral differences for 10 K vs 20 K deposition
As stated in the main text, when the more CO rich 2% mixture is used for 10 K deposition (Figure 4B),
the results are qualitatively similar to those measured following deposition of the 100-fold more dilute
0.02% CO mixture at 20 K (c.f. Fig 2), however, there are some small but significant differences. First,
there is a slight but consistent and reproducible blue-shifting of most of the peaks by 0.2-0.3 cm-1 in the
10 K spectrum (c.f. Table I), with the exceptions being the Cu(CO) 3- peak (not shifted) and the Cu(CO)3
peak at 1985.5 cm-1 (redshifted by 0.4 cm-1 from 20 K spectrum). Additionally, there are new bands at
1774 cm-1 and 1824 cm-1, which are tentatively assigned (based on proximity) to di- and tricarbonyl
complexes trapped in different matrix sites at the lower deposition temperature. There are also partially
resolved features at 1981.4 and 1983.4 cm-1 that grow in upon annealing to 20 K; although there is
intensity in the corresponding region of the 20 K deposition spectrum (c.f. Fig. 2), it is harder to identify
individual bands. Note also that most of the impurity bands are absent from the spectra in Fig. 4B; the
deposition gas for this sample was run through a liquid nitrogen/ethanol bath, in order to remove the
metal carbonyl contaminants. The only remaining peaks in the region where impurities were observed are
at 2039 cm-1, which is from 13C18O (observable in this high-concentration CO mix at natural abundance),
and at 2048 cm-1, which cannot be assigned at this time. It does not seem to correspond to any known
complex of CO in argon, yet its intensity scales with CO concentration (c.f. Fig 3) and it is not removed
by cryogenic trapping of the matrix gas. It is near the position of the (CO) 2+ peak in neon matrices (2051
cm-1 2), which was observed in laser ablation studies of copper carbonyls, however the corresponding
peak in argon matrices was not observed.3
Ion abundance calculation
Using the ion beam currents and the physical dimensions of the matrix, we can estimate the number
density of ions in the matrix, assuming unity probability of ion trapping in a homogeneous matrix.
Deposition at 10 nA for 2 hours corresponds to delivery of 4.6x1014 each of cations and anions; based on
the etalon peaks in the infrared spectra (supporting info Fig. S4) the matrix thickness is estimated to be 60
mm, assuming this is uniform over the deposition area of 3.1 cm2 yields a matrix volume of 0.018 cm3,
corresponding to a number density of ~2.5x1016 ions/cm3 each for cations and anions. Using the bulk
density of solid argon (~1.77 g/cm3 at 20K 1), this converts to a molar Cu-:Ar ratio of ~1:106, representing
an upper limit for the ion concentration in the matrices presented here. Of course the actual ion
abundance is likely significantly lower in practice, given expected losses due to phenomena such as
“grounding out” of ions on the sample holder, as well as scattering in local high pressure of the deposition
region. The spectra presented in the main text also reveal significant populations of neutral species upon
deposition, indicating that many of the ions undergo neutralization as the matrix is forming.
Table S1. Peaks assigned to transitions from metal carbonyl impurities (c.f. Fig 2-4 of main paper), based
on previous spectroscopic assignments (see references contained within4,5). Peaks marked with ‘?’ do not
correspond to any previously reported bands, but are still assigned to impurity species based on their
absence when using an ethanol cooling bath, and insensitivity to annealing (note their absence in
difference spectra in Fig. 4B of main paper).
Impurity Peaks
Absorption Assignment
1998.2
?
2001.1
?
2003.95
Fe site
2006.12
2008.8
2009.98
2023.2
Fe(CO)5
?
?
?
2025.4
2034.6
Fe(CO)5
?
2051.7
Ni(CO)4
References
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(2) Jacox, M. E.; Thompson, W. E., Res. Chem. Intermed. 12, 33 (1989).
(3) Zhou, M.; Andrews, L., J. Chem. Phys. 111, 4548 (1999).
(4) Zhou, M.; Andrews, L.; Bauschlicher, C. W., Chem. Rev. 101, 1931 (2001).
(5) Zhou, M.; Chertihin, G.; Andrews, L., J. Chem. Phys. 109, 10893 (1998).