Experimental absolute cross sections for the reaction of isobutane [CH(CH3)3] with [CH2O]•+ isomers

Abstract

Isomers frequently exhibit different physical and chemical properties, which can make accurate modeling of their reactivity highly challenging but can also be exploited as a method for isomer identification. In both cases, this requires accurate experimental data recorded at an isomer-specific level. The reactions of the DCOH•+ and H2CO•+ ions with isobutane [CH(CH3)3] are investigated experimentally in the 0.07–10 eV collision energy range using a guided-ion beam tandem mass spectrometer coupled to a tunable vacuum ultraviolet source. The reaction of the DCOH•+ ion is dominated by dissociative proton transfer processes, while the reactivity of H2CO•+ is predominantly driven by dissociative charge transfer processes. The kinematics are also significantly different, with the overall reactivity of the DCOH•+ isomer following an approximately Langevin trend, while the reactivity of H2CO•+ is distinctly non-Langevin. In addition, for the H2CO•+ isomer, sharp changes in reactivity are observed at photon energies corresponding to Rydberg autoionization, leading to vibrational excitation of the C–O stretching mode. The findings highlight the inadequacy of modeling molecular ions as point charges and evidence the need for isomer-specific reactivity data.