TY - JOUR
T1 - Small gas-phase dianions produced by sputtering and gas flooding
AU - Franzreb, Klaus
AU - Williams, Peter
N1 - Funding Information:
This work was supported by the National Science Foundation under Grant No. CHE 0111654. Jan Lörinčík provided the sample and assisted with the negative SIMS measurements on and on flooded Ce.
PY - 2005
Y1 - 2005
N2 - We have extended our previous experiment [Schauer, Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of Cn 2- (n≥7) by means of sputtering a graphite surface by Cs+ ion bombardment. Our detection sensitivity for small Cn 2- could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C5 2- was not successful. As an upper limit, the sputtered flux of C5 2- must be at least a factor of 5000 lower than that of C7 2-, provided that the lifetime of C5 2- is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O2 or with N2 O) was supplied to the Cs+ -bombarded graphite surface, small dianions of OCn 2- (5≤n≤14) and O2 C7 2- were observed in addition to Cn 2- (n≥7). Similarly, Cs+ sputtering of graphite with simultaneous SF6 gas flooding produced SCn 2- (6≤n≤18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF6 gas flooding of various Cs+ -bombarded metal surfaces were successful for the case of Zr, where metastable ZrF6 2- was observed. Cs+ bombardment of a silicon carbide (SiC) wafer produced SiCn 2- (n=6, 8,10). When oxygen gas was supplied to the Cs+ -bombarded SiC surface, small dianions of SiOCn 2- (n=4, 6,8) and of SiO2 Cn 2- (n=4, 6) as well as a heavier unidentified dianion (at mz=98.5) were observed. For toluene (C7 H8) vapor flooding of a Cs+ -bombarded graphite surface, several hydrocarbon dianion clusters of Cn Hm 2- (n≥7) were produced in addition to Cn 2- (n≥7), while smaller Cn Hm 2- with n≤6 could not be observed. BeCn 2- (n=4, 6,8,10), Be2 C6 2-, as well as BeC8 Hm 2- (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs+ -bombarded beryllium metal foil. The metastable pentamer Be9 C4 2- 12 at mz=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SCn 2-, OCn 2-, BeCn 2-, and SiOm Cn 2- (m=0, 1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeCn 2- and SiCn 2-, even though calculated molecular structures of BeC6 2- and SiC6 2- are different. The abundance pattern of SCn 2- is fairly similar to that of Cn 2-.
AB - We have extended our previous experiment [Schauer, Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of Cn 2- (n≥7) by means of sputtering a graphite surface by Cs+ ion bombardment. Our detection sensitivity for small Cn 2- could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C5 2- was not successful. As an upper limit, the sputtered flux of C5 2- must be at least a factor of 5000 lower than that of C7 2-, provided that the lifetime of C5 2- is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O2 or with N2 O) was supplied to the Cs+ -bombarded graphite surface, small dianions of OCn 2- (5≤n≤14) and O2 C7 2- were observed in addition to Cn 2- (n≥7). Similarly, Cs+ sputtering of graphite with simultaneous SF6 gas flooding produced SCn 2- (6≤n≤18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF6 gas flooding of various Cs+ -bombarded metal surfaces were successful for the case of Zr, where metastable ZrF6 2- was observed. Cs+ bombardment of a silicon carbide (SiC) wafer produced SiCn 2- (n=6, 8,10). When oxygen gas was supplied to the Cs+ -bombarded SiC surface, small dianions of SiOCn 2- (n=4, 6,8) and of SiO2 Cn 2- (n=4, 6) as well as a heavier unidentified dianion (at mz=98.5) were observed. For toluene (C7 H8) vapor flooding of a Cs+ -bombarded graphite surface, several hydrocarbon dianion clusters of Cn Hm 2- (n≥7) were produced in addition to Cn 2- (n≥7), while smaller Cn Hm 2- with n≤6 could not be observed. BeCn 2- (n=4, 6,8,10), Be2 C6 2-, as well as BeC8 Hm 2- (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs+ -bombarded beryllium metal foil. The metastable pentamer Be9 C4 2- 12 at mz=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SCn 2-, OCn 2-, BeCn 2-, and SiOm Cn 2- (m=0, 1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeCn 2- and SiCn 2-, even though calculated molecular structures of BeC6 2- and SiC6 2- are different. The abundance pattern of SCn 2- is fairly similar to that of Cn 2-.
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U2 - 10.1063/1.2136154
DO - 10.1063/1.2136154
M3 - Article
AN - SCOPUS:29144531214
SN - 0021-9606
VL - 123
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 22
M1 - 224312
ER -