Intracluster Ion−Molecule Reactions of Ti⁺with Methanol Clusters

Abstract

The intracluster ion-molecule reactions occurring within the titanium/methanol heterocluster ions are studied using a simple cluster source based on the mixing of the laser-ablated plasma with the supersonic expansion of a methanol vapor seeded in Ar carrier gas. The product ions are detected using a reflectron time-of-flight mass spectrometer. The mass spectra exhibit a major sequence of cluster ions with the formula Ti + (CH 3 O) 2 (CH 3 -OH) n , which are attributed to the hydrogen elimination reactions (-2H or -H 2 ) of Ti + ion within the heteroclusters. In addition, heterocluster ions of the types Ti + (CH 3 O)(CH 3 OH) n and Ti + (CH 3 O) 3 (CH 3 OH) n also emerge throughout the observed mass spectra, indicating that consecutive H-eliminations by the Ti + ion occur for up to three methanol molecules. The results from isotope-labeling experiments suggest that H-elimination is the reaction path for O-H bond breaking in Ti + -methanol heteroclusters. The observed TiOH + and TiO + ions are interpreted as arising from the insertion of Ti + ions into the C-O bond in CH 3 OH, followed by CH 3 -and CH 4 -elimination, respectively, from the [HO-Ti + -CH 3 ] intermediate. The experiments also show that the chemical reactivity of heterocluster ions is greatly influenced by cluster size and argon stagnation pressure. The reaction energetics and formation mechanisms of the observed heterocluster ions are also discussed.

Intramolecular Ion-Molecule Reactions within Ti+(CH3COCH3)nHeteroclusters: Oxidation Pathway via C=O Bond Activation

“…8,11,12 The observation of peaks corresponding to TiO + indicated that the reaction was initiated by the insertion of Ti + into the C=O bond of an acetone molecule. We postulate that product formation proceeded through the reactions given below.…”

“…The experimental details of the ion-molecule reaction dynamics measurements have been described previously; [8][9][10] therefore, only a brief description is given here. Ti + ions were generated by focusing the third harmonic (355 nm) of a Nd:YAG laser onto a rotating titanium disk, with an illumination area of diameter ~0.5 mm.…”

“…36 It might be argued that sequential H elimination reactions via C-H bond insertions occurred in several CH 3 COCH 3 molecules within a heterocluster, which is the major reaction pathway in the reactions of Ti + with ethanol and dimethyl ether. 8,10 Unfortunately, the ions (Ti + (C3H4O)(CH3COCH3)n) (H eliminations from single acetone molecule) and (Ti + (C3H5O)2(CH3COCH3)n-1) (H eliminations from two acetone molecules) were difficult to distinguish because of their identical masses. However, the absence of Ti + (C3H5O)(CH3COCH3)n product ions in the mass spectrum of Figure 2 indicated that H2 elimination occurred in a single CH3COCH3 molecule only.…”

“…[6][7] During the last few years, we have studied the intracluster ion-molecule reactions of Ti + with various organic molecules (water, alcohols, and esters) with the goal of elucidating the reactivity of Ti + ions and the reaction pathways that lead to heterocluster complex formation. [8][9][10][11][12][13] In particular, the reaction pathways of intracluster ion-molecule reactions of Ti + with ether clusters ((CH3OR)n, R = CH3, n-C3H7, n-C4H9, t-C4H9) appeared to vary depending on the alkyl group in the ether molecule. 10 The major sequences of heterocluster ions with the formulas Ti + (OCH 3 ) m (OR) n (m = 1-3 and n = 0-2) were attributed to the insertion of Ti + ions into the C-O bonds of the ether molecules within the heteroclusters, followed by alkyl radical elimination.…”

“…Moreover only a few studies have examined the chemical reactions occurring within the heterocluster ion itself. [8][9][10][11][12][13] In the present study, we have investigated the reaction of Ti + with C=O, C-C, and C-H bonds in acetone molecules within heterocluster ions. The main purpose of this work was to develop a quantitative interpretation of the reaction mechanism suggested by our observations.…”