Wan Yong Feng

Evaporation of dimers from proton-bound acetic acid clusters

Abstract Proton-bound clusters of acetic acid and mixed clusters of acetic acid and water evaporate neutral dimers of acetic acid. This attribute is shared with liquid acetic acid. Clusters are considered to bridge the gap between the gas phase and condensed phases. The evaporation of dimers begins to be observed with the heptamer. Cluster binding energies to monomer and dimer units were deduced from kinetic energy releases. The values for the low members of the series are in quite good agreement with previous data from high pressure mass spectrometry. Kinetic energy releases were remeasured and re-evaluated also for proton-bound formic acid clusters. Thermochemical cycles lead to the following bond energies of the evaporated neutral dimers: 0.58 ± 0.07 eV for acetic acid and 0.66 ± 0.13 eV for formic acid. These values indicate, contrary to previous conclusions, that the neutral dimers evaporate in the ring-closed, two hydrogen-bonded, form.

Reactions of proton-bound dimers

Thermal reactions of proton-bound dimers, (CH3CN)2H +, (CH3OCH3)2H +, and (CH3COCH3)2H+, were studied using a selected ion flow tube. Reactions observed include association, switching, and proton transfer. The association channel was observed only for base molecules that had hydrogen bonding protons such as NH3, CH3NH2, (CH3)2NH, and CH3OH. An association-insertion mechaniSoc was proposed in which the central proton of the symmetrically bound dimers is replaced by a protonated base, for example, NH4+. These reactions are relatively slow, which demonstrates a central barrier along the potential energy surface. Ether-containing dimers do not demonstrate this insertion reaction, except for diethers, for example, CH3OCH2CH2OCH3, which can form stable bicyclic structures. Dimers such as (HCOOH)2H+, which possess hydrogen bonding protons in the periphery, undergo switching reactions with ammonia and no insertion.

Ion/molecule reactions of naphthalene and 1-chloronaphthalene radical cations

Abstract Reactions of the naphthalene radical cation, C10H8·+, and the 1-chloronaphthalene radical cation, C10H7Cl·+, with a series of small organic molecules including amines, alcohols, ethers and simple carbonyl compounds have been studied by the selected ion flow tube (SIFT) technique. Observed reactions for the naphthalene cation include the associated adduct with hydrogen atom elimination from the reactant ion or neutral, association without elimination and charge transfer. Reaction products of the naphthalene cation were identified by running isotopomeric reactions with deuterated naphthalene. Reactions of the chloronaphthalene cation are association with hydrogen atom, chlorine atom or hydrogen chloride molecule elimination from the adducts, association without elimination and charge transfer. Reaction channels depend on the ionization energy of the reactant and vary in the above order with decreasing ionization energy of the neutral. C10H7Cl·+ is generally more reactive than C10H8·+. Most of the reactions are very slow except for charge transfer reactions with trimethylamine and triethylamine. No proton transfer channel takes place for any of the primary reactions. A naphthyne containing ion adduct is formed in the reaction of C10H7Cl·+ with some molecules due to HCl elimination from the primary adduct.

Multiply hydrogen bonded complexes in ether systems: combining experiments with density functional theory calculations

Abstract Reactions of proton bound dimers of dimethyl ether (DME), (CH 3 OCH 3 ) 2 H + studied previously are compared with those of proton bound dimers of tetrahydrofuran (THF), (c-C 4 H 8 O) 2 H + . Experiments were carried out on a selected ion flow tube (SIFT). Base molecules having protic hydrogens such as NH 3 , CH 3 NH 2 , and Me 2 NH, which are capable of forming multiply hydrogen bonded core ions, undergo insertion into the THF dimer but not into the DME dimer. The potential energy profiles for the association-insertion reactions of ammonia with both dimers were calculated using the density functional theory (DFT) at the B3LYP/cc-pVTZ level of theory. The insertion of ammonia into (DME) 2 H + or (THF) 2 H + demonstrates high central barriers in double-well potential energy profiles. RRKM/QET rate constant calculations on the two surfaces give results which are in agreement with the experimental branching ratios between the reaction channels of insertion and switching.