Time‐of‐flight mass spectrometric analysis of ion formation in hypervelocity impact of organic polymer microspheres: comparison with secondary ion mass spectrometry, ²⁵²Cf mass spectrometry and laser mass spectrometry

Abstract

Unisized 1.6-microm polystyrene microspheres coated with PEDOT (polyethylene-dioxythiophene) were accelerated to speeds of 6-16 km/s and shot onto a silver target. Either positive or negative ions, both instantaneously formed by the impact process, have been analyzed by time-of-flight mass spectrometry (TOF). Apparently, the processes that control the formation of ions of either polarity depend on the impact velocity. Comparing the results with those of secondary ion mass spectrometry with primary ion energy in both the elastic and the inelastic ((252)Cf-MS) energy loss regimes, some reaction mechanisms of the polymer ions for different energy densities could be elucidated. Some aspects of ion formation are also related to those found in pulsed laser ion generation from these microspheres. This investigation was performed in order to further improve the method of analyzing the organic fraction of interstellar, interplanetary, and cometary dust particles impinging on the targets of the "CIDA" time-of-flight (TOF) mass spectrometers on-board the NASA comet missions "STARDUST" and "CONTOUR".

Time of flight mass spectra of ions in plasmas produced by hypervelocity impacts of organic and mineralogical microparticles on a cosmic dust analyser

“…Since our mass spectra at low speed appear similar to those of Brenna et al (1991), we adopt the approach of attempting to assign an identification associated with the observed m/z values and correlate these with either structure in the original particle or for example carbon clusters. We agree with Kissel & Krueger (2001) in that at impact speeds between 10 and 20 km s −1 this structure changes, but noting the results of Hinz et al (1994) we again make tentative chemical identifications based on the observed m/z values rather than suggest the observation of unstable ions which decomposed during acceleration. It should be noted however, that both interpretations explain the change in the mass spectra above m/z = 100 as the impact speed increases from 10 to 20 km s −1 .…”

“…For some mass numbers it would be possible to make the assignment of a carbon cluster. However, whilst Kissel & Krueger (2001), observe carbon clusters in negative ion mass spectra using similar particles, they comment that the production of such clusters is favoured for negative ions and thus such signals are not expected in positive ion mass spectra as obtained here. In the intermediate velocity regime (Table 6), the impact energy per projectile is sufficient to destroy most of the larger molecular ions (i.e.…”

“…It has been shown in preliminary work that these particles can be used in laboratory-based impact ionization experiments that incorporate time-of-flight mass spectrometry. Goldsworthy et al (2002) showed that the particles can yield mass spectra (in a Cassini CDA type detector), and Kissel & Krueger (2001) showed that mass spectra can be obtained from an instrument similar to that used on the Stardust space mission.…”

“…There are also impact ionization data for both positive and negative ion mass spectra for polyethylene-dioxythiophene coated polystyrene particles (Kissel & Krueger 2001). In their positive ion mass spectra, at low speeds (6 km s −1 ) the only line they specifically associate with the particle (as against contaminants)is that at m/z = 91 (the tropylium cation), they see no higher mass series of peaks.…”

Time-of-flight mass spectrometry of mineral volatilization: Toward direct composition analysis of shocked mineral vapor

“…Studies using electrostatically accelerated microparticles have also been carried out in which impactgenerated ions were analyzed in situ using time-of-flight mass spectrometry. 5,[24][25][26][27][28][29][30][31] These studies have been limited to metal, polymer, and coated particles, and have not studied minerals of interest to the question of chemical speciation in impacts. Kawaragi used mass spectrometry and isotopic labeling to identify the gaseous species produced in pressed calcium carbonate powder samples shocked using a laser-accelerated flyer plate.…”