Mobilities of Aromatic Ions Drifting in Helium

Abstract

Aromatic ions are produced in an electron impact ion source and injected into the flow tube section of a selected-ion flow-drift tube (SIFDT) apparatus. The reduced mobilities of C6H5 +, C6H6 +, C6H7 +, C12H12 +, C12H11 +, naphthalene (C10H8 +) cation, and biphenyl (C12H10 +) cation drifting in helium are measured as a function of the characteristic parameter E/N (the ratio of the electric field to the number density of the helium buffer gas atoms in the drift tube). The reduced mobilities of the benzene dimer ions (C12H12 + and C12H11 +) are compared with the measured mobilities of naphthalene and biphenyl cations to correlate the mobilities with ionic structures. An angle-averaged collision cross section of the ions drifting in helium is obtained from the geometric structure of these ions and is used to compute the zero-field mobility. The predicted zero-field mobilities are found to compare well with the experimentally measured mobilities.

Mobility of t-C4H9+ in polar and nonpolar atmospheric gases

“…The mobility values remain relatively constant over the range of E=N studied in the buffer gases He, N 2 and O 2 , indicating that the interaction potential is dominated by repulsive forces, as expected for nonpolar buffer gases. The experimental mobility of C 4 H þ 9 in helium is consistent with the mobilities for larger hydrocarbons in helium, both experimentally and theoretically, when ion structure is included in the calculations [13]. For example, the experimental ion mobilities of C 6 H þ 6 and C 12 H þ 12 in He are 11.8 AE 0.3 and 7.6 AE 0.3 cm 2 V À1 s À1 , respectively.…”

“…The experiments are performed using a drift tube system that is slightly modified from our original selected ion flow drift tube (SIFDT) from previous experiments [3,[13][14][15]17]. Ions are created by electron impact and mixed with a buffer gas in the flow tube region where a positive voltage of 50 V is applied for approximately 40 cm, repelling negative ions.…”

“…For example, the experimental ion mobilities of C 6 H þ 6 and C 12 H þ 12 in He are 11.8 AE 0.3 and 7.6 AE 0.3 cm 2 V À1 s À1 , respectively. The ion mobilities of C 6 H þ 6 and C 12 H þ 12 in He, calculated by the angle-averaged hard sphere cross-section method, where ion structure is included, are 11.4 and 7.6 cm 2 V À1 s À1 , respectively [13], while K pol values are 17.4 and 17.1 cm 2 V À1 s À1 , respectively. Clearly the inclusion of ion structure is essential for accurate mobility calculations.…”

Ion Dynamics Related to Hypersonics

“…Much of this interest arises from the need to obtain a better understanding of the transport of ions in discharges, lasers, semiconductor plasma processing, and various phenomena in the earth's atmosphere. Using flow tube techniques and arrival time measurements, we have determined the mobilities of aromatic ions 24 and of many atmospheric cluster ions. 21 " 23 Using Doppler resolved laser-induced fluorescence, we have examined the velocity distributions and molecular alignment of ions in drift fields.…”

Laser-based ion mobility spectrometry for sensing of aromatic compounds

“…[13][14][15] Combined with quantum chemical calculation methods, providing structure proposals, and with improved models for the calculation of diffusion cross sections, 10,16 a powerful tool for structure determination of gas phase ions has been created. 17 In this work, REMPI and IM spectra of several PAH and alkylbenzenes are presented. The experimentally determined diffusion cross sections (Ω exp ), directly obtained from ion mobilities (cf.…”