Probing trapped ion energies via ion-molecule reaction kinetics: Quadrupole ion trap mass spectrometry

Abstract

We present a detailed study of the energies of the ions stored in a quadrupole ion trap mass spectrometer (QITMS). Previous studies have shown that the rate constant, k, for the charge exchange reaction Ar(+) N(+) 2 →, N(+) 2+Ar increases with increasing ion-molecule center-of-mass kinetic energy (K.E.cm). Thus, we have determined k for this chemical "thermometer" reaction at a variety of Ar and N2 pressures and have assigned K.E.cm values as a function of the q2 of the Ar(+) ion both with and without He buffer gas present in the trap. The K.E.cm energies are found to lie within the range 0.11-0.34 eV over the variety of experimental conditions investigated. Quantitative "cooling" effects due to the presence of He buffer gas are reported, as are increases in K.E.cm due to an increase in the q2 of the Ar(+) ion. "Effective" temperatures of the Ar(+) ions in He buffer are determined based on a Maxwell-Boltzmann distribution of ion energies. The resulting temperatures are found to lie within the range ≈ 1700-3300 K. We have also examined the K.E.cm, values arising from the chemical thermometer reaction of O(+) 2 with CH4, as previous assignments of effective ion temperatures based on this reaction have been called into question.

Theoretical calculations for mass resolution of a quadrupole ion trap reflectron time‐of‐flight mass spectrometer

“…The measurements were carried out using a sophisticated experimental method where the temperature was determined by measuring the rate constants of bimolecular or unimolecular reactions whose temperature dependence had been established by other means 27, 28. Applying this method to the bimolecular reaction of Ar + /N 2 , Yost and coworkers27 reported that the temperature of Ar + was very high – in the range of 1700–3300 K. On the other hand, pointing out several possible reasons for the previously reported high ion temperature in a QIT, Gronert29 insisted that the temperature of the ions was close to that of the buffer gas by comparing the equilibrium constant measured for the complexation reaction of thiophenolate with 2,2,2‐trifluoroethanol with the literature value for the thermochemistry. He also cited some previous theoretical and experimental results supporting his argument.…”

Quadrupole ion trap studies of fundamental organic reactions

“…In early work, the kinetics of the reaction of CH 4 with O 2 þ was used to probe the effective temperature of ions in a quadrupole ion trap (Nourse & Kenttamaa, 1990;Basic, Eyler, & Yost, 1992). This system had been studied in the past under a wide range of conditions so a correlation between reaction rate and ion energy was already well established.…”

Ion/Molecule reactions in SiH4/H2S and GeH4/H2S mixtures

“…In the case of reactions of S + , the ground electronic state is a quartet ( 4 S), while the first excited state is a doublet ( 2 D or 2 P). Therefore, we assign the endothermic reactions (1) and (2) to the S + ( 4 S) ions translationally excited, due to the RF trapping field inside the ion trap 32, 37, 55. On the other hand, reactions (3) and (4) are spin‐allowed for the electronically excited S + ( 2 D or 2 P) ions.…”

“…Reaction (1) was chosen for ion gauge calibration in GCQ as it is a well‐known reaction: it is one of the most ever studied ion/molecule reactions involving more than three atoms, and its rate constant has been reported by several authors 35. In early 1990s, it was employed for determination of effective ion temperatures in quadrupole ion traps 36, 37. However, Viggiano et al 38 showed that particular care must be adopted when employing such reaction as a reference system, for its rate constant may significantly change according to reactants' energy.…”