Surface Impact Dissociation of Neutralized Ions: Studying Unimolecular Gas-Phase Reactions in the Context of Cassini INMS Data

Brigham Young University Engineering Building, Provo, UT

Analysis of spaceborne analytes using mass spectrometers is complicated by hypervelocity impacts (v > 6 km s^-1), which induce dissociative scattering of analyte molecules and obscure compositional signatures. However, neutral dissociative scattering remains poorly understood due to the lack of controlled experimental data. To address this gap, we are developing the Surface Impact Neutralization Dissociation Instrument (SINDI), a laboratory platform that reproduced and analyzes these processes under controlled conditions. SINDI implements a two-stage experiment. First, mass-selected ions are accelerated onto a gold-plated surface to induce neutralization and dissociation. Second, following dissociation, the resulting neutral fragments are adsorbed onto a gold-plated aluminum cryotrap, then thermally desorbed and analyzed using Evolved Gas Analysis Mass Spectrometry (EGA-MS) with a 5–15 °C min^-1 thermal ramp. To ensure reproducible thermal desorption, we characterized the cryotrap's temperature uniformity under atmospheric conditions: at 24–36 V, the root-mean-square deviation (δT_RMS) between the body and endcaps remains below 2 °C. Once fully operational, SINDI will enable controlled investigation of neutral dissociative scattering in the context of extraterrestrial mass spectrometric analysis.