Small gas-phase dianions produced by sputtering and gas flooding

Abstract

We have extended our previous experiment [Schauer et al., Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of C(n) (2-)(n > or =7) by means of sputtering a graphite surface by Cs(+) ion bombardment. Our detection sensitivity for small C(n) (2-) could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C(5) (2-) was not successful. As an upper limit, the sputtered flux of C(5) (2-) must be at least a factor of 5000 lower than that of C(7) (2-), provided that the lifetime of C(5) (2-) is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O(2) or with N(2)O) was supplied to the Cs(+)-bombarded graphite surface, small dianions of OC(n) (2-)(5< or =n < or =14) and O(2)C(7) (2-) were observed in addition to C(n) (2-)(n > or =7). Similarly, Cs(+) sputtering of graphite with simultaneous SF(6) gas flooding produced SC(n) (2-)(6< or =n< or =18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF(6) gas flooding of various Cs(+)-bombarded metal surfaces were successful for the case of Zr, where metastable ZrF(6) (2-) was observed. Cs(+) bombardment of a silicon carbide (SiC) wafer produced SiC(n) (2-) (n=6,8,10). When oxygen gas was supplied to the Cs(+)-bombarded SiC surface, small dianions of SiOC(n) (2-) (n=4,6,8) and of SiO(2)C(n) (2-) (n=4,6) as well as a heavier unidentified dianion (at mz=98.5) were observed. For toluene (C(7)H(8)) vapor flooding of a Cs(+)-bombarded graphite surface, several hydrocarbon dianion clusters of C(n)H(m) (2-)(n> or =7) were produced in addition to C(n) (2-)(n> or =7), while smaller C(n)H(m) (2-) with n< or =6 could not be observed. BeC(n) (2-) (n=4,6,8,10), Be(2)C(6) (2-), as well as BeC(8)H(m) (2-) (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs(+)-bombarded beryllium metal foil. The metastable pentamer (9)Be(12)C(4) (2-) at mz=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SC(n) (2-), OC(n) (2-), BeC(n) (2-), and SiO(m)C(n) (2-) (m=0,1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeC(n) (2-) and SiC(n) (2-), even though calculated molecular structures of BeC(6) (2-) and SiC(6) (2-) are different. The abundance pattern of SC(n) (2-) is fairly similar to that of C(n) (2-).

Parity alternation of linear ground-state CnS2− (n=6–18) clusters

“…8, the values of E I vary according to a pattern of odd/even alternation: when n is even, the E I value is large; when n is odd, the E I is small. Because a larger E I value implies a more stable C n S 2− structure, one can deduce that a C n S 2− cluster with even n is more stable than one with odd n. Such odd/even alternation of electron detachment (EDE and SEDE) and incremental binding energy is in consistency with the experimental observation of Franzreb and Williams [26]. It can be explained by a combined consideration of the overall behaviors of electron detachment (EDE and SEDE) and the incremental binding energies of the dianionic clusters.…”

“…In the dianion abundance patterns of SC n 2− (6 ≤ n ≤ 18) anions for SF 6 flooding of graphite [26], the dianionic clusters show an obvious odd/even behavior: the dianions with even number of carbon atoms are more prominent. To explore the experimental observation theoretically, we designed many structural models of C n S 2− (n = 6-18), and performed geometry optimization and calculations on vibrational frequencies by means of the B3LYP density functional method.…”

Structure of the doubly charged C5O22− anion

“…In particular 1, 3, and 4 can be prepared by deprotonating fairly standard organic compounds. Finally, let us mention that the dianion C 7 O 2 2− that also has been detected by Franzreb and Williams [33] can be explained in terms of the same type of structures. As for C 5 O 2 2− , there will be several electronically stable isomers that can be derived from isomers 1 to 6 by inserting C 2 groups into the structures.…”

On the formation of SFn– (n = 1–6) anions via a novel route and their properties

“…Middleton also attempted to spray SF 6 gas in combination with Kr gas at a titanium sputter‐surface to generate KrF – anions . Sputtering and SF 6 gas flooding were also used by Franzreb et al to produce molecular anions composed of target atoms and/or gas‐phase atoms, identifying dianions of SC n 2– (n = 6–18), ZrF 6 2– and the SF – anion …”