Comprehensive site-specific probabilities for bond rearrangement in ethanol photofragmentation

Ethanol (CH₃CH₂OH) has three non-equivalent sites for hydrogen atoms: the hydrogen that is part of the hydroxyl group, the three β-hydrogens attached to the carbon atom opposite the hydroxyl group, and the two α-hydrogens attached to the central carbon atom. Bond rearrangement initiated by an ultrafast laser pulse, leading to hydrogen-rich photofragments such as H₃⁺, can involve hydrogen atoms from all three sites. Using COLTRIMS experiments examining different deuterium-tagged isotopologues of ethanol under the same laser pulse conditions (800 nm central wavelength, 3.0×10¹⁴ W/cm² peak intensity, 23 fs FWHM), we measure the relative probabilities of producing H₃⁺, CH₄⁺, H₂O⁺, and H₃O⁺ as a function of the initial sites of the hydrogen atoms that compose the final products. These site-specific measurements provide a new benchmark for molecular dynamics calculations.