Design and Characterization of a Custom Cryotrap for Use in Neutralizing Impact Dissociation Studies

Orem, UT

Identification of parent molecules sampled during hypervelocity flybys requires distinguishing impact-induced from ionization-induced fragmentation within the antechamber of a closed-source Ion and Neutral Mass Spectrometer (INMS). To characterize the neutral products of surface-impact dissociative scattering, we have developed the Surface-Impact Neutralizing Dissociation Instrument (SINDI), which condenses volatile neutral fragments at cryogenic temperatures for subsequent thermal desorption and mass spectral analysis. A functional cryotrap is crucial for understanding the unimolecular-dissociation reactions that occur during impact; however, our original cryotrap design suffered from poor thermal coupling between the coolant line and trap body, reaching a minimum temperature of only 225 K with an average cooling rate of 1.2 K/min. The redesigned cryotrap utilizes copper cooling tubing press-fit into precision-machined grooves on a gold-plated aluminum body, which increased the contact area between the body and copper tubing from 0.71 cm² to 55.2 cm²—an improvement of roughly 78-fold over the original surface-wrapped design. Cryotrap cooling rates improved from 1.2 K/min to 38 K/min (32-fold improvement), with the minimum attainable temperature decreasing from approximately 225 K to 110 K. Evolved Gas Analysis (EGA) of n-hexane confirmed successful analyte retention at cryogenic temperatures and controlled thermal desorption, with the molecular ion (m/z 86) and characteristic fragment ions (m/^{z 43, 57) detected during the thermal desorption. These results demonstrate that the redesigned cryotrap meets the thermal performance requirements for use as a means of capturing neutral fragments in SINDI experiments.}