Experimental\nCharacterization of the Isomer-Selective\nGeneration of the Astrochemically Relevant Hydroxymethylene Radical\nCation (HCOH<sup>•+</sup>/DCOH<sup>•+</sup>)

Interest in the observation and characterization of organic\nisomers\nin astronomical environments has grown rapidly with an increase in\nthe sensitivity of detection techniques. Accurate modeling and interpretation\nof these environments require experimental isomer-specific reactivity\nand spectroscopic measurements. Given the abundance of formaldehyde\n(H<sub>2</sub>CO) in various astrophysical objects, the properties\nand reactivities of its cation isomers H<sub>2</sub>CO<sup>•+</sup> and HCOH<sup>•+</sup> are of significant interest. However,\nfor the hydroxymethylene radical cation HCOH<sup>•+</sup> (and\nits isotopologue DCOH<sup>•+</sup>), detailed reactivity studies\nhave been limited by the lack of suitable experimental methods to\ngenerate this isomer with high purity. Here, potential approaches\nto the isomer-selective generation of HCOH<sup>•+</sup> and\nDCOH<sup>•+</sup> are characterized through differential reactivity\nmeasurements. While the dissociative photoionization of cyclopropanol\n(c-CH<sub>2</sub>CH<sub>2</sub>CHOH) is determined to be unsuitable,\nthe dissociation of methanol-<i>d</i><sub>3</sub> (CD<sub>3</sub>OH) allows for the formation of DCOH<sup>•+</sup> with\na fractional abundance of >99% at photon energies below 14.8 eV.\nThese\nresults will allow future spectroscopic and reactivity measurements\nof HCOH<sup>•+</sup>/DCOH<sup>•+</sup> to be conducted,\nlaying the groundwork for future detection and incorporation into\nmodels of the interstellar medium.