Toshiharu Mori

Formation and stabilities of cluster ions Ar+n

Temperature dependence of the rate constants for the clustering reaction, Ar+(2P3/2)+2Ar=Ar+2(2Σ+u)+Ar, was measured in the temperature range 300–55 K using a pulsed electron‐beam mass spectrometer. The rate constant shows a steady increase with decrease of temperature, from 2.0×10−31 cm6/s at 300 K to 7×10−31 cm6/s at 55 K. The metastable atomic ion Ar+(2P1/2) was found to start to form the cluster ion Ar+2 below 130 K. The thermochemical stabilities of the cluster ions Ar+n were also determined with n=3–11. A sudden drop in the −ΔH0n−1,n values was observed between n=3 and 4, indicating that the Ar+3 ion is the core in the cluster Ar+n.

Stability of rare gas cluster ions

Thermochemical values, ΔH0n−1,n and ΔS0n−1,n, for clustering reactions, Rg+n−1+2Rg=Rg+n+Rg (Rg=He, Ne, Kr, and Xe), were measured with a pulsed electron‐beam mass spectrometer. The −ΔH0n−1,n values show a sudden decrease between n=3 and 4, for all rare gases suggesting that the core ion in Rg+n is Rg+3. The values −ΔH0n−1,n with n=3 are found to be in the order Ne<He<Ar<Kr<Xe, and those with n≥4 in the order of atomic radii.

Isotope effect and nature of bonding in the cluster ions H+3(Ar)n and D+3(Ar)n

Thermochemical data, ΔH○n−1,n and ΔS○n−1,n (n=1–7), of clustering reactions, H+3(Ar)n−1+Ar=H+3(Ar)n and D+3(Ar)n−1+Ar=D+3(Ar)n, were measured with a pulsed electron‐beam high‐pressure mass spectrometer. The shell formation with n=3 and 6 was observed for both H+3(Ar)n and D+3(Ar)n clusters. The binding energies of D+3(Ar)n are found to be about 0.2 kcal/mol greater than those of H+3(Ar)n with n=1–3. With n≥4, the binding energies for both clusters become about the same. The Ar ligands in the cluster D+3(Ar)n are found to have slightly more restricted freedoms of motion than those in H+3(Ar)n, probably due to the smaller size of the core ion D+3 than H+3. The binding energy of H+3‐‐‐Ne was also measured. The obtained binding energy (∼0.4 kcal/mol) is more than one order of magnitude smaller than that of H+3‐‐‐Ar (6.69 kcal/mol). This is mainly due to the much smaller polarizability of Ne than Ar. A careful remeasurement of thermochemical data for the clustering reaction H+3+H2=H+3(H2) was also made. The ob...

Gas-phase stability and structure of cluster ions CH5+(CH4)n with n=1-9

Abstract Thermochemical data, Δ H n -1, n 0 and Δ S n -1, n 0 , for the clustering reactions CH 5 + (CH 4 ) n -1 + CH 4 =CH 5 + (CH 4 ) n , with n =1-9 were measured using a pulsed electron-beam mass spectrometer. Both −Δ H n -1, n 0 and −Δ S n -1, n 0 show irregular decreases between n =2 and 3, and 7 and 8, the latter indicating the formation of a shell structure, CH 5 + (CH 4 ) 2 (CH 4 ) 5 .

Thermochemical stabilities of D3+ (D3)n with n = 1–10

Abstract The equilibria for the clustering reaction D 3 + (D 2 ) n −1 + D 2 = D 3 + (D 2 ) n were studied over the temperature range 300-25 K using a pulsed electron-beam high-pressure mass spectrometer. The thermochemical stabilities of D 3 + (D 2 ) n with n = 1–10 were determined. The bond energies of D 3 + (D 2 ) n were found to be greater than those of H 3 + (H 2 ) n for all n measured, but the differences are less than 0.2 kcal/mol. Successive shell formation for the clusters D 3 + (D 2 ) n with n = 3, 6, 8, and 10 is suggested.

The gas-phase solvation of C2H+5, s-C3H+7, and s-C4H+9 with CH4. The isomeric structures of C2H+5 and C2H+5…CH4

Abstract The gas-phase equilibria of the clustering reactions of C 2 H + 5 , s -C 3 H + 7 , and s -C 4 H + 9 with CH 4 were studied with a pulsed electron-beam high-pressure mass spectrometer. The bond energies of the clusters s -C 3 H + 7 (CH 4 ) n and s -C 4 H + 9 (CH 4 ) n are nearly n -independent. In contrast, there is an irregular decrease in the bond energies for the clusters C 2 H + 5 (CH 4 ) n between n = 1 and 2. It is found that the non-classical C 2 H + 5 isomerizes to the classical one during the clustering reaction of C 2 H + 5 with CH 4 and the terminal methyl protonated propane is formed.

Gas-phase solvation of N+2 with Ar atoms: a charge switch in the reaction N+2 + Ar → Ar+ …N2

Abstract In order to examine the solvating strength toward a cation species N + 2 , the equilibria of clustering reactions N + 2 (Ar) n − 1 + 2Ar = N + 2 (Ar) n + Ar were studied with a pulsed electron beam high-pressure mass spectrometer. the thermochemical stabilities of N + 2 (Ar) n with n ⩾ 2 were determined. The bond energies of N + 2 (Ar) n show an irregular decrease with n = 2 → 3 and those with n ⩾ 3 become almost n independent. Through ab initio MO calculations, the above irregular decrease can be verified theoretically in terms of an anomalous switch of the charge center, N + 2 + Ar → N 2 …Ar + .

On the formation of the isomeric cluster ions (CO)+n

The kinetics and equilibria of clustering reactions (CO)+n−1+CO=(CO)+n (n=3–18) were studied, using a pulsed electron‐beam high‐pressure mass spectrometer. It was found that there are two isomers for the tetramer (CO)+4. The energy barrier for the isomerization reaction was measured to be 6.1 kcal/mol. Anomalous van’t Hoff plots for the clustering reactions were obtained with n=8–10, probably due to the existence of several isomeric cluster ions. The structures of the cluster ions (CO)+n with n=2–5 were examined by ab initio MO calculations. Two core ions of n=3, σ and π radical cations, are found to give different clustering patterns.

Gas phase stabilities of cluster ions H+(CO)2(CO)n, H+(N2)2(N2)n and H+(O2)2(O2)n with n=1–14

Abstract Thermochemical stabilities of H + (CO) 2 (CO) n , H + (N 2 ) 2 (N 2 ) n and H + (O 2 ) 2 (O 2 ) n with n electron-beam high-pressure mass spectrometer. The H + (CO) 2 (CO) n cluster with n =4 has been found to form a rather solid first shell indicating the participation of covalent bond in the shell. For the H + (N 2 ) 2 (N 2 ) n clusters the shell formation with and 7 is suggested. The H + (O 2 ) 2 (O 2 ) n cluster with n =1 has been found to be much more stable than those with n ⩾2. The ion may be represented as H + (O 2 ) 3 (O 2 ) 2 (O 2 ) n . The ring structure for the core ion H + (H 2 ) 3 has been proposed.