Evidence of CF2 Loss from Fluorine-rich Cluster Anions Generated

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Evidence of CF Loss from Fluorine-rich Cluster Anions Generated from Laser Ablation of Graphite Fluoride Brett A. Williams, Allen R. Siedle, and Caroline Chick Jarrold J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b09983 • Publication Date (Web): 30 Nov 2018 Downloaded from http://pubs.acs.org on December 4, 2018

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The Journal of Physical Chemistry

Evidence of CF2 Loss from Fluorine-rich Cluster Anions Generated from Laser Ablation of Graphite Fluoride Brett A. Williams, Allen R. Siedle, and Caroline Chick Jarrold* Department of Chemistry, Indiana University, 800 E. Kirkwood Ave, Bloomington, IN 47405

ABSTRACT A mass spectrometric analysis of the anionic and cationic species generated by laser ablation of graphite fluoride (GF) and graphite targets performed under identical sets of conditions is presented. Under conditions that produce typical Cn cluster mass distributions from ablation of graphite, the mass spectra of anionic species generated by ablation of GF are congested with overlapping stoichiometric patterns such as CnF2n and CnF(2n-2). Some of the molecular formulas for these clusters, such as C6F6, C6F12, and C7F8, are evocative of stable neutral fluorocarbons. Additionally, the GF-ablation generated mass peaks broaden at higher masses more than the graphite-based counterparts, which may indicate cluster fragmentation. Furthermore, a pattern of fragmentation via loss of CF2 is observed, and is reminiscent of previous studies which determined CF2 loss during thermal decomposition. No species were seen in the mass spectra of the cationic species generated from laser ablation of GF, while under the same conditions, typical Cn+ cluster distributions were observed.

* C. C. Jarrold. E-mail: [email protected]. Phone: (812) 856-1190. Fax: (812)855-8300. https://orcid.org/0000-0001-9725-4581

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I. Introduction Vaporization and subsequent condensation of carbon has led to a diversity of new nanostructures, the most prominent of which are the fullerenes.1-2 Other studies have decisively characterized the gas phase species produced in the vaporization process.3-9 We report here our studies on the laser vaporization of graphite fluoride (GF), an electrode material in lithium ion batteries.10-16 GF is a white, wide band gap solid produced by direct fluorination of graphite.12, 17 The lamellar material retains the six membered rings of its precursor but, because addition of fluorine changes carbon hybridization from sp2 to sp3, they are no longer planar, extended, zero band gap conducting sheets.12,17 Additional structural details are debated, but the material can be described as a series of layers in which each layer is a network of 6-membered chair structured rings in which the F atoms project into the van der Waals gaps.17-18 The interlayer spacing, 5.76Å, is much larger than in graphite. The C–F bond energy is estimated to be 115 kcal/mole, approximately the same as in fluorocarbons,19 and the C–C bond length is increased from 1.41 Å in graphite to 1.47 Å in GF.18 Collectively, these metrical data are consistent with GF having single C–C bonds relative to the stronger C- -C bonds in graphite, as well as having substantially reduced interlayer attractions. As an electrode material, thermal decomposition of GF is of considerable interest. A study by Kamarchik and Margrave17 found that decomposition proceeds by loss of (CF2)n units, leaving graphitic regions with very different electronic structures within the remaining GF material. Laser ablation provides an environment of violent, hyperthermal decomposition, motivating the current study of laser vaporization of GF. To compare the GF ablation-generated species to a well-known system, we performed side-by-side comparisons with those generated by ablation of graphite. Under conditions that have been found to generate typical Cn cluster distributions in the 2 ≤ n ≤ 60 range, we find that laser ablation of GF results in formation of distinct families of CnFm fluorocarbanions in the lower mass- and higher mass regions of the mass spectrum. In the lower mass region, high abundances of C6F C7F8, and C6F12, which are evocative


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of perfluorinated benzene, toluene and cyclohexane, are observed, in addition to (and overlapping with) a series of stoichiometric GF anion clusters [(CF)n, n = 5–10], two series of peaks separated by 12 amu/e (CnF6, n = 4 – 6) and (CnF8, n = 5 – 9), and a series of peaks separated by 19 amu, C6Fm (m = 6 – 12). While there are clearly favored anions, the stoichiometries are largely statistical, suggesting they form by coalescence of atoms and/or small molecules in the ablation source. In contrast, patterns in the higher mass region are much simpler, while the peaks are broadened and embedded in continuum signal. The patterns observed exhibit mass intervals consistent with loss of 50 amu CF2 units. Combined with the peak broadening and continuum signal, a picture of large clusters formed by direct desorption followed by internal energy dissipation via CF2 loss emerges. This hyperthermal CF2 loss is evocative of thermal decomposition of GF observed in bulk studies.

II. Methods The apparatus used in this study has been described in detail previously.20-21 Briefly, Cn and CnFm cluster anions and cations were generated using a laser ablation/pulsed molecular beam valve source. Hydraulically pressed graphite [Asbury Carbons, 95% min.] and GF [Daikin, C1F1.08] targets were ablated with 2 mJ/pulse of the second harmonic output of a Continuum Surelite I Nd:YAG laser (532 nm, 2.33 eV, 9 ns pulse) operated at a repetition rate of 30 Hz focused onto the surface of the rotating target. Higher laser powers were used but were found to almost immediately obliterate the target. The resulting plasma was entrained in a pulse of ultrahigh purity (UHP) He carrier gas (30 psig stagnation pressure, 120 μs pulse) and swept along a 25-mm long, 3-mm diameter channel into a vacuum chamber. The gas plume was collimated by a 3-mm diameter skimmer, and the anions or cations were accelerated on axis in a constant electric field and subsequently referenced to ground using the potential switch method.22 The anions or cations continued into a 1.2-m Bakker-style beam-modulated time-of-flight23-24 (BM-TOF) mass spectrometer and were subsequently detected by a dual microchannel plate (MCP) detector assembly.



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Delaying the ablation laser pulse trigger relative to the molecular beam valve affects the ion production conditions; increasing the delay increases the pressure of He present when the plasma is produced, which increases the cluster size, presumably because of enhanced thermalization of nascent species. Varying the time of the potential switch relative to the ablation laser pulse selects different portions of the gas plume expanding from the source; earlier switch times select for lighter species, and later switch times select heavier species. The beam modulation plate (BMP) trigger time relative to the potential switch time also selects certain portions of the gas plume that passes through the potential switch. Mass spectra of clusters generated from both the graphite and GF were measured under several sets of source conditions and mass spectrometer settings, specified in the following manner: The timing of the ablation laser trigger, A, relative to the gas pulse trigger, T0, the potential switch trigger, B, relative to the ablation laser trigger (A), and the BMP trigger, C, relative to the potential switch trigger (B) can be expressed as: A = T0 + t

[1]

B = A + t′

[2]

C = B + t″

[3]

The trigger timings and the mass ranges of the clusters detected are given in Table 1. In short, the A delay governs which clusters are produced, while the B and C delays govern which portion of the expansion is observed. In this experiment, mass spectra were obtained for the ablation products of graphite and GF under the same source conditions for both anionic and cationic species.

III. Results Figure 1 shows characteristic mass spectra of cluster anions generated from the ablation of (a) graphite and (b) GF targets. In Fig. 1(a), the progression of carbon cluster anions (Cn) in the mass range shown is broad and contains a typical cluster distribution with magic numbers, though the conditions have not been optimized for C60 production. Fig. 1(b) shows the mass spectrum of the GF cluster anions (CnFm)


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recorded using identical source conditions and mass spectrometer settings. Several prominent species can be discerned in the congested mass spectrum, including C6F6, C7F8, C7F14, C8F16, and C10F18. The clusters generally become more fluorine-rich at higher mass. The species observed have higher mass distributions than those observed in previous studies on laser ablation of polytetrafluoroethylene, but given our use of a clustering channel, this is not unexpected.25 In addition, patterns of stoichiometries that follow incremental mass differences that coincide with CF2 units are observed (vide infra). A preliminary observation is that several peaks in the high mass region of the mass spectra for the GF ablation products are broader than the lower-mass peaks, beyond what can be attributed to the constant m/Δm relationship for this type of mass spectrometer, and they are broader than the carbon cluster peaks of similar masses. In addition, there is more pronounced continuum signal within the manifold of CnFm mass peaks when compared to the mass spectrum of the graphite-generated Cn cluster mass spectrum. Figure 2(a) shows the mass spectrum of GF-generated CnFm clusters overlaid on an expanded scale with the graphite-generated Cn clusters. Comparing ions with similar mass, the ratio of the full-width halfmaximum (FWHM) of the C6F12 to C25 mass peaks is 2.0 and C7F12 is 2.3 times broader than C26. C7F14 is 1.6 times broader than C29, which can be seen more clearly in Fig. 2(b), which shows the peaks shifted to lie on top of each other. Note that the 12C2813C isotopomer is partially resolved from the 12C29 mass peak (black trace) while the C7F14 mass peak (red trace) envelopes both carbon cluster mass peaks. Broadening indicates broader ion energy spread prior to entering the acceleration region or cluster fragmentation during ion acceleration into the TOF region. Table 2 summarizes the hypothetical kinetic energy spread that would be consistent with the peak width for several mass peaks produced by ablation of graphite and GF. The CnFm clusters would have to have approximately twice the energy spread as the Cn clusters to account for the observed peak width disparity. Because the ablation conditions and mass spectrometer settings were the same when measuring both mass spectra, the kinetic energy spread, and therefore the peak widths, for similarly sized clusters



should be approximately the same. Indeed, because the CnFm clusters have fewer carbon atoms than pure carbon clusters with the comparable mass (e.g., C7F14 versus C29), they should in fact appear narrower, since there is less isotopomer spread from 13C. We therefore consider the possibility that the CnFm clusters may be undergoing fragmentation in the acceleration region of the mass spectrometer. Fragmentation of clusters can occur when the internal energy of the cluster is higher than the threshold for bond dissociation.26-34 Fragmentation of an ion in the acceleration stack will result in a continuum of drift times for the daughter ions, ranging between the expected drift time for an ion with the daughter mass, td, and the drift time expected for the parent, tp. Assuming first order kinetics, the probability of fragmentation is highest when the ion enters the acceleration stack, which would result in a daughter ion drift time of td, and exponentially decreases in time. Therefore, the number of daughter ions generated between the entrance and exit of the acceleration stack, which appear between td and tp, decreases as the parent ion progresses through the stack, resulting in the appearance of an exponentially decaying tail of ion signal to higher drift times from td. In order to determine if fragmentation is consistent with the appearance of the peaks in the 300-525 amu/e region of the mass spectrum, a simulation was performed and compared to the mass spectrum for GF ablation (Figure 3). There were two basic assumptions used to simplify this simulation. First, each peak represents the sum of the initial ion clusters formed from laser ablation, some of which do not have sufficient internal energy to fragment, and clusters formed from parent ion decay. Second, each daughter ion with mass mi results from a single parent ion with mass Mi = mi + 50 amu fragmenting into the daughter ion and a CF2 neutral fragment.17 Loss of CF2 is consistent with patterns in the mass spectrum, seen below. Simulations were performed using a home-written LabVIEW code (S1, S2). The probability of fragmentation of a parent ion at a particular place in the acceleration stack is a parameter determined by the mass of the ion, the length of the acceleration stack, and a first order decay rate constant (s-1). The time traveled from the source to the acceleration stack can be varied in the code,


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which allows for control of the proportion of daughters appearing in the mass spectrum at td (unaffected by decomposition in the acceleration stack) versus those appearing at later time due to production in the acceleration stack. Figure 3 shows an example of a simulation (red trace) superimposed on the experimental mass spectrum (black trace), assuming a decay rate constant of 3.0 x 104 s1, giving a half-life of 23.1 μs, which is comparable to what has been reported for carbon cluster ions.27, 29-30 The time between the source and acceleration region is set to a physically reasonable value of 25 μs. While the fit is not perfect, the sum of the exponentially decaying tails in drift times from td does result in continuum signal between the mass peaks, similar to what is observed experimentally. Therefore, fragmentation in the acceleration region under these conditions is not discounted as an explanation for the peak broadening.

IV. Discussion Given that fragmentation in the acceleration region is supported by the results, we now consider the implications of the mass assignments. Figure 4(a) and 4(b) show the mass spectrum of the CnFm clusters on an expanded scale over the mass range of 125 amu/e to 525 amu/e with several mass assignments indicated. A striking feature of the mass spectrum is that the lower mass range (Fig. 4(a)) is more congested than the higher mass range (Fig. 4(b)), which shows very distinct, more abundant “magic” ions and patterns of cluster masses separated by 50 amu, equivalent to the mass of CF2. Assignments of ions in the lower mass portion of the mass spectrum (125 amu/e to 325 amu/e) was facilitated by identifying series of masses with 12 amu/e or 19 amu/e separation. Among them are a series of stoichiometric GF anion clusters [(CF)n, n = 5–10], two series of peaks separated by 12 amu/e (CnF6, n = 4 – 6) and (CnF8, n = 5 – 9), and a series of peaks separated by 19 amu, C6Fm (m = 6 – 12). We note here that several of the more abundant ions in this mass range, C6F C7F8, and C6F12, suggest retention of the 6-membered ring structure in the bulk, with these masses coinciding with hexafluorobenzene, perfluorotoluene, and perfluorocyclohexane. 7 ACS Paragon Plus Environment


Again, the m/Δm of peaks in this lower-mass portion of the mass spectrum is higher than those in the higher-mass portion, and the wide range of compositions additionally suggests they form by atomization of the GF followed by coalescence in the clustering channel of the ablation source. However, we note that, despite the high electron affinity of carbon clusters, we do not observe elemental carbon clusters, though there are species that are very carbon-rich (possible assignments of all peaks, including those not indicated by the combs in Fig. 4 are included in the supporting information). In addition, the molecular species suggested by C6F C7F8, and C6F12 have relatively low neutral electron affinities (e.g., 0.72 eV for C6F6),35 so their high abundance in the mass spectrum would reflect particularly high neutral stability and abundance. The fact that species with higher binding energies, e.g., open shell neutrals, are slightly less intense further supports the relatively high abundance of the closed-shell neutrals. In the higher-mass portion of the mass spectrum (275 amu/e to 525 amu/e), there are several distinct peak patterns in which the ions are separated by 50 amu/e, again corresponding to the mass of CF2, several of which are shown. The series of peaks can be described with the formula CnF2nx (x = 0 – 3, series with higher values of x being less intense) with the most prominent ions having CnF2n (n = 6  10) and CnF(2n-2) (n = 7 – 11). The prevalence of these patterns may suggest that CF2 loss from more massive clusters with high internal energy is occurring. The picture that emerges from these results is that the ions are formed in at least two fundamentally different ways: (1) Ablation forms atomic or small molecular species that coalesce in the ion source, and (2) large species with high internal energy are directly desorbed from the GF target, and subsequently undergo CF2 loss. This latter mode is evocative of previous studies which show that when heated, GF decomposes into various fluorocarbons, the most prominent of which is CF2.17,36 It also implies that the larger desorbed species passivate their broken bonds with F-atoms generated in the atomization of the material, making them F-rich.


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The principal conclusions of this analysis of the GF ablation product mass spectrum is that the higher masses are fluorine rich, the lower mass region has species approaching the bulk GF stoichiometry, there are clear series of masses separated by the mass equivalent of CF2, and there are signatures in the mass spectrum consistent with parent ion fragmentation in the acceleration stack. Finally, we note that in a previous study, cationic products were detected from the slow-heating decomposition of GF, though only with ionization energies of 16 eV and above.36 We therefore measured the mass spectra in positive ion mode for ablation products of both graphite and GF. Figure 5 shows a direct comparison of mass spectra measured in cation mode (blue traces) and anion mode (black traces) for (a) graphite ablation products and (b) GF ablation products. Fig. 5(a) shows that C3+ dominates the mass distribution of cationic clusters generated from graphite ablation under low-mass conditions (offset blue trace, indicated with *), whereas the mass spectrum for the graphite ablation under high-mass conditions is consistent with what has been observed previously, giving a range of cations comparable to the anions.4-5 In Fig. 5(b), only Fe+ generated from the sample mount is observed from ablation of GF under low-mass conditions, and in the high mass region, no cluster cations were observed or were distinguishable from the baseline. This result suggests that the GF material does not absorb sufficient energy in the ablation to ionize the species to the cationic state.

It is also possible that the high abundance of F combined with high

pressure buffer gas results in charge combination.

V. Conclusions The mass spectra of anions generated by intensely hyperthermal laser ablation of GF exhibit fluorocarbon clusters with a range of stoichiometries over the mass range of 150-550 amu. Large, fluorinerich clusters are generated at higher masses and exhibit relatively simple mass patterns spaced by CF2. Ion signal in the lower mass range is more congested with carbon rich species. These observations, combined with intense continuum signal over the intermediate mass range and broader mass peaks compared to the pure carbon cluster control data, suggests fragmentation of larger anions during ion acceleration via loss of CF2. This fragmentation is evocative of the method of graphite fluoride decomposition proposed by 9 ACS Paragon Plus Environment


Kamarchik and Margrave, which involves (CF2)n loss and results in a fluorine-depleted graphitic material.17 Several of the more abundant anions observed have molecular formulas corresponding to stable neutral fluorocarbons, such as C6F6, C6F12, and C7F8.38-42 These observations raise several questions about the structures of the CnFm clusters which we hope to study in the future. No cationic clusters were observed from ablation of GF, despite cations being produced and detected in previous conventional thermal decomposition studies,36 while the ion source did produce typical distributions of carbon cluster cations from ablation of graphite.4-5 ASSOCIATED CONTENT Supporting Information: The Supporting Information includes a block diagram of the LabVIEW code used in the simulations of mass spectrometric peak shapes resulting from fragmentation of ions in the acceleration stack of the mass spectrometer and a table that includes the masses of all ions observed in the mass spectrum of ions generated from laser ablation of GF, with possible assignments. AUTHOR INFORMATION Corresponding Author *C.C. Jarrold. E-mail: [email protected]. Phone: (812) 856-1190. Fax: (812) 855-8300. Notes The authors declare no competing financial interest. ACKOWLEDGEMENTS This work was supported in its entirety by the U.S. Department of Energy, Office of Basic Energy Sciences, under Award No. DE-FG02-07ER15889, and was performed at Indiana University, Bloomington. CCJ thanks Prof. Liang-shi Li at Indiana University for helpful discussions.


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LIST OF FIGURES Figure 1. Mass spectra of ions generated from ablation of (a) graphite and (b) GF. Peaks are labeled n in (a) and n,m in (b), where n is the number of carbon atoms, and m is the number of fluorine atoms Figure 2. (a) High mass portion of mass spectra of ions generated by ablation of graphite (black) and GF (red). n is the number of carbon atoms, m is the number of fluorine atoms. (b) The C29 (black) and C7F14 (red) aligned to illustrate disparate peak widths. Figure 3. Mass spectrum of ions generated from ablation of GF (black trace) with simulation based on first order decay of larger clusters by loss of 50 amu (red trace). See text for details. Figure 4. Patterns of ions generated from ablation of GF target in the (a) 125 to 325 amu mass range and (b) 275 to 525 amu mass range. A comprehensive list of all ion assignments is included in the supporting information. Figure 5. Comparison of anions (black) and cations (blue) generated by ablation of (a) graphite and (b) GF. The inset mass spectra were obtained using settings to collect the low-mass region of the spectrum (see Table 1).


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Page 15 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 Time delays between the various triggers for systematic study. For each value of t, several mass spectra were measured for incrementally increasing values of t′. The values of t″ were varied to produce the cleanest mass spectrum in the low mass region. For t = 100–200 μs, the cluster mass range was 0–132 amu/e (low mass region) and for t = 300–400 μs, the cluster mass range was 60–1164 amu/e (high mass region). t (μs) 100, 150, 200

300, 350, 400

t′ (μs) 210 220 230 240 320 340 360 380 380 400

t″ (μs) 1-2.5 1.4-2.7 1.6-3.8 1.6-3.9 3-4 4 5-6 6 12 7

Mass Range (amu/e) 0-48 0-96 36-108 48-132 60-276 60-540 84-996 84-1072 372-1164 144-1056

Table 2 Hypothetical values for kinetic energy spread in eV for the peaks in Figure 2, consistent with the FWHM ratios in the text.

Graphite target GF target

Cluster C25 C26 C29 C6F12 C7F12 C7F14

ΔKE (eV) 2.84 2.55 2.78 5.67 5.68 4.27



15 (a) Cn

30

40 8 50 Relative Ion Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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7,8

7,14 8,16 10,18

6,6

0

(b) CnFm

50 100 150 200 250 300 350 400 450 500 550 600 650 700

Mass/Charge (amu/e)

Figure 1. Mass spectra of ions generated from ablation of (a) graphite and (b) GF. Peaks are labeled n in (a) and n,m in (b), where n is the number of carbon atoms, and m is the number of fluorine atoms

ACS Paragon Plus Environment

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(a) 25,0

27,0

6,12

29,0

7,14

340

350

7,12

Relative Ion Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


300

310

320

330

(b) GF target Graphite target

342 344

344 346

346 348

348 350

350 352

352 354

354 356


Figure 2. (a) High mass portion of mass spectra of ions generated by ablation of graphite (black) and GF (red). n is the number of carbon atoms, m is the number of fluorine atoms. (b) The C29 (black) and C7F14 (red) aligned to illustrate disparate peak widths. ACS Paragon Plus Environment

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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275

300

325

350

375

400

Mass/Charge

425

450

475

500

525

550

(amu/e)

Figure 3. Mass spectrum of ions generated from ablation of GF (black trace) with simulation based on first order decay of larger clusters by loss of 50 amu (red trace). See text for details.


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4

5

6

5

CnF6

125

5

6

150

6

7

8

7

175

9

8

200

9

225

(a) Low mass

CnF8

8

7

6


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9 10

250

10 12

(CF)n C6Fm

300

325

11

275

(b) High mass 7

6 7

8 8

9

8

300

325

375

11

10

8

350

10 10

9

7

275

9

11

9

400

425

475


Figure 4. Patterns of ions generated from ablation of GF target in the (a) 125 to 325 amu mass range and (b) 275 to 525 amu mass range. A comprehensive list of all ion assignments is included in the supporting information. ACS Paragon Plus Environment

CnF(2n-3)

10

450

CnF2n CnF(2n-2)

CnF(2n-1)

500

525


2.5

(a) Graphite 2.0

1.5

*

Cation mode

1.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

0.5

0.0

*

Anion mode

0

50

100 150 200 250 300 350 400 450 500 550 600

2.5

(b) GF

2.0

*

Cation mode

1.5

1.0

Anion mode

*

0.5

0

50

100 150 200 250 300 350 400 450 500 550 600


Figure 5. Comparison of anions (black) and cations (blue) generated by ablation of (a) graphite and (b) GF. The inset mass spectra were obtained using settings to collect the low-mass region of the spectrum (see Table 1). ACS Paragon Plus Environment

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Page 21 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


125

150

175

200 225 250 Mass/Charge (amu/e)

275

TOC graphic


300

325

Evidence of CF2 Loss from Fluorine-rich Cluster Anions Generated

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