10.2 Reactivity of Met-Cars
165
10.2 Reactivity of Met-Cars
Since the discovery as a new cluster species referred to Metallo-Carbohedrenes in
1992 [57, 58], reasonable research interest has been stimulated to elucidate the physical and chemical properties of this new species. Researchers utilized metastable
decay, collision-induced dissociation, and photo-dissociation techniques to probe
the bonding and dissociation patterns of the Met-Cars. Interestingly, Ti 8 C 12
+ was
found to be inert toward oxygen etching reaction. Further, the reactions of Ti 8 C 12
+
had been studied under thermal energy conditions and a high gas pressure at 0.7 Torr
within a selected ion drift tube reactor (SIDT) [65].
Figure 10.1a shows a typical product distribution acquired from the reaction
of Ti 8 C 12
+ with acetone. It was noted that, based on a multiple-step attachment
process, one to five acetone molecules bind to Ti 8 C 12
+ leading to the adducts Ti 8 C 12
+
(C 3 H 6 O) 1–5 . The multiple attachment processes of acetone onto Ti 8 C 12
+ can be
represented as,
Ti 8 C
+
12 + xC 3 H 6 O → Ti 8 C
+
12 (C 3 H 6 O) x
(10.1)
where x was observed to be 1 to 5. In comparison, the reaction of Ti 8 C 12
+ with methyl
iodide (CH 3 I) yields rare association products, as shown in the mass spectrum of
Fig. 10.1b. The only apparent peak as numbered corresponds to the product Ti 8 C 12 I
+ .
There were no changes when varying the pressures of MeI from 0.2 to 0.8 mTorr. This
reaction process indicates the dissociation of CH 3 I, which differs from an association
reaction as Eq. 10.1 but resembles the reactivities of pure Al
−
n clusters and Al n I
−
x
species toward CH 3 I in the flow tube reactor [77, 78]. The selective reactivity of the
Ti 8 C 12
+ is still elusive and open to further exploration.
However, the reactivity of Met-Cars with methanol is different from the reactivity
towards acetone and methyl iodide. It was worth mentioning that Ti 8 C 12
+ takes up
eight methanol molecules, as shown in Fig. 10.2a, b. In the case of a very low partial
pressure of methanol being presented, the reaction terminates at eight methanol
attachments. Similarly, this multiple attachment processes of methanol onto Ti 8 C 12
+
can be represented as,
Ti 8 C
+
12 + xCH 3 OH → Ti 8 C
+
12 (CH 3 OH) x
(10.2)
where x was observed to be 1 to 8. However, at a much higher pressure of methanol,
all the species Ti 8 C 12
+ (CH 3 OH) 0–7 disappeared while Ti 8 C 12
+ (CH 3 OH) 8 interestingly survives and dominates the entire mass spectrum, as shown in Fig. 10.2b. This
observation demonstrated reasonable activity of Ti 8 C 12
+ and the unique stability
of Ti 8 C 12
+ (CH 3 OH) 8 where the eight sites of Ti atoms were taken by attaching
methanol molecules one by one. As the oxygen atom of a methanol molecule has
a lone pair electron, its electronegativity renders the chemisorption of methanol on
Ti 8 C 12
+ through an O–Ti bond. No products of Ti 8 C 12
+ (CH 3 OH) x>8 were observed,
165
10.2 Reactivity of Met-Cars
Since the discovery as a new cluster species referred to Metallo-Carbohedrenes in
1992 [57, 58], reasonable research interest has been stimulated to elucidate the physical and chemical properties of this new species. Researchers utilized metastable
decay, collision-induced dissociation, and photo-dissociation techniques to probe
the bonding and dissociation patterns of the Met-Cars. Interestingly, Ti 8 C 12
+ was
found to be inert toward oxygen etching reaction. Further, the reactions of Ti 8 C 12
+
had been studied under thermal energy conditions and a high gas pressure at 0.7 Torr
within a selected ion drift tube reactor (SIDT) [65].
Figure 10.1a shows a typical product distribution acquired from the reaction
of Ti 8 C 12
+ with acetone. It was noted that, based on a multiple-step attachment
process, one to five acetone molecules bind to Ti 8 C 12
+ leading to the adducts Ti 8 C 12
+
(C 3 H 6 O) 1–5 . The multiple attachment processes of acetone onto Ti 8 C 12
+ can be
represented as,
Ti 8 C
+
12 + xC 3 H 6 O → Ti 8 C
+
12 (C 3 H 6 O) x
(10.1)
where x was observed to be 1 to 5. In comparison, the reaction of Ti 8 C 12
+ with methyl
iodide (CH 3 I) yields rare association products, as shown in the mass spectrum of
Fig. 10.1b. The only apparent peak as numbered corresponds to the product Ti 8 C 12 I
+ .
There were no changes when varying the pressures of MeI from 0.2 to 0.8 mTorr. This
reaction process indicates the dissociation of CH 3 I, which differs from an association
reaction as Eq. 10.1 but resembles the reactivities of pure Al
−
n clusters and Al n I
−
x
species toward CH 3 I in the flow tube reactor [77, 78]. The selective reactivity of the
Ti 8 C 12
+ is still elusive and open to further exploration.
However, the reactivity of Met-Cars with methanol is different from the reactivity
towards acetone and methyl iodide. It was worth mentioning that Ti 8 C 12
+ takes up
eight methanol molecules, as shown in Fig. 10.2a, b. In the case of a very low partial
pressure of methanol being presented, the reaction terminates at eight methanol
attachments. Similarly, this multiple attachment processes of methanol onto Ti 8 C 12
+
can be represented as,
Ti 8 C
+
12 + xCH 3 OH → Ti 8 C
+
12 (CH 3 OH) x
(10.2)
where x was observed to be 1 to 8. However, at a much higher pressure of methanol,
all the species Ti 8 C 12
+ (CH 3 OH) 0–7 disappeared while Ti 8 C 12
+ (CH 3 OH) 8 interestingly survives and dominates the entire mass spectrum, as shown in Fig. 10.2b. This
observation demonstrated reasonable activity of Ti 8 C 12
+ and the unique stability
of Ti 8 C 12
+ (CH 3 OH) 8 where the eight sites of Ti atoms were taken by attaching
methanol molecules one by one. As the oxygen atom of a methanol molecule has
a lone pair electron, its electronegativity renders the chemisorption of methanol on
Ti 8 C 12
+ through an O–Ti bond. No products of Ti 8 C 12
+ (CH 3 OH) x>8 were observed,