Development of lithium attachment mass spectrometry - knudsen effusion and chemical ionisation mass spectrometry (KEMS, CIMS).

Lithium ion attachment mass spectrometry provides a non-specific, non-fragmenting, sensitive and robust method for the detection of volatile species in the gas phase. The design, manufacture and results of lithium based ion attachment ionisation sources for two different mass spectrometry systems are presented. In this study trace gas analysis is investigated using a modified Chemical Ionization Mass Spectrometer (CIMS) and vapour pressure measurements are made using a modified Knudsen Effusion Mass Spectrometer (KEMS). In the Li+ CIMS, where the Li+ ionization acts a soft and unselective ionization source, limits of detection of 0.2 ppt for formic acid, 15 ppt for nitric acid and 120 ppt for ammonia were achieved, allowing for ambient measurements of such species at atmospherically relevant concentrations. In the first application of Lithium ion attachment in ultra-high vacuum (UHV), vapor pressures of various atmospherically relevant species were measured with the adapted KEMS, giving measured values equivalent to previous results from electron impact KEMS. In the Li+ KEMS vapour pressures <10-3 mbar can be measured without any fragmentation, as is seen with the initial electron impact (EI) set up, allowing the vapor pressure of individual components within mixtures to be determined.

Dissociation energetics of the phenol(+)⋯Ar(2) cluster ion: The role of π→H isomerization.

The dissociation energetics in the phenol(+)⋯Ar(2)(2π) cluster ion have been investigated using photoionization efficiency and mass analyzed threshold ionization spectroscopy. The appearance energies for the loss of one and two Ar atoms are determined as ∼210 and ∼1115 cm(-1), respectively. The difference between the appearance energy for the first Ar ligand in phenol(+)⋯Ar(2)(2π) and the dissociation energy of the phenol(+)⋯Ar(π) dimer (535cm(-1)) is explained by the isomerization of one π-bound Ar ligand to the OH binding site (H-bond) upon ionization. The energy difference between phenol(+)⋯Ar(2)(2π) and phenol(+)⋯Ar(2)(H/π) could also be estimated to be around 325cm(-1), which corresponds roughly to the difference of the binding energy of a π-bound and H-bound Ar ligands. The binding energy of the H-bound Ar atom in phenol(+)⋯Ar(2)(H/π) is derived to be ∼905cm(-1).