Absolute cross sections for the formation of OH- from 2-propanol (CH3CH(OH)CH3) via dissociative electron attachment (DEA) are reported in the incident electron energy range of 3.5-13 eV. Four fragment anions are observed: OH-, C2H2O-, C2H4O-, and C3H7O-. The OH- yield exhibits a pronounced resonance centered at 8.2 eV together with a broader structure extending over the 8-10 eV region. Equation-of-Motion Coupled-Cluster (electron attached) calculations with Singles and Doubles combined with a Complex Absorbing Potential (CAP/EOM-EA-CCSD) assign this feature to a two-particle-one-hole (2p-1h) core-excited Feshbach resonance. Potential energy curves along the C-OH dissociation coordinate reveal that core-excited anion states in this energy range promote efficient cleavage of the hydroxyl group. Analysis of Dyson orbitals and resonance widths demonstrates that only states with repulsive antibonding sigma(C-OH) character and sufficiently long lifetimes contribute significantly to the observed OH- production. These results provide fundamental insight into the DEA dynamics of secondary alcohols and highlight the role of multi-electron-attached resonances in site-specific bond rupture induced by low-energy electrons.
Electron-driven processes, particularly dissociative electron attachment (DEA), are fundamental to understanding molecular degradation in diverse fields such as radiation chemistry, astrochemistry, and plasma physics [1][2][3][4][5]. DEA is a two-step resonant process in which a low-energy electron attaches to a molecule, forming a transient negative ion (TNI), provided a suitable resonant state exists. The TNI may undergo auto detachment by releasing the electron; dissociation occurs only if it survives [1,6]. These two pathways compete with each other. The energy dependence of DEA cross sections is governed by the Franck-Condon overlap between the neutral ground state and the anionic resonance potential energy surface, which determines the probability of attachment at specific electron energies [7,8]. Furthermore, the lifetime of the TNI with respect to autodetachment is critically influenced by the coupling between the resonance state and the continuum, as well as the number of vibrational degrees of freedom available for energy redistribution [4,5].
In DEA, TNI resonances lead to bond cleavage, with significant implications for radiation damage in biological systems [9], beyond dipole transitional state preparations [10], and molecular evolution in interstellar media. Alcohols serve as key model systems for studying these mechanisms.
The secondary alcohol 2-propanol (isopropanol) is of specific interest due to its dual relevance as a sustainable fuel blend [11] and as a structural analogue to ribose sugars in RNA, aiding studies of radiation-induced damage. Furthermore, its detection in the interstellar medium [12] underscores the need to characterize its electron-induced chemistry. While DEA to primary alcohols like methanol and ethanol has been extensively studied [13][14][15][16][17][18][19][20][21][22][23], data for secondary alcohols remain sparse. For the structural isomer 1-propanol, several DEA studies exist [24,25], but for 2-propanol, only limited DEA data have been reported, noting a spectral shift of -4.1 eV relative to the photoelectron spectrum [25].
This scarcity motivates the present comprehensive investigation. Here, we report a combined experimental and theoretical study of OH -formation from 2-propanol via DEA in the 3.5-13 eV range. Using high-resolution time-of-flight mass spectrometry and the Relative Flow Technique (RFT), we measured absolute cross sections and identify resonance structures. These findings are interpreted with high-level theoretical calculations using the CAP-EOM-EA-CCSD method, which provides potential energy curves along the C-OH dissociation coordinate and reveals a dense manifold of anion states. Through Dyson orbital analysis and survival probability estimates, we assign the resonances responsible for OH - formation, notably linking the prominent 8.2 eV feature to a 2p1h core-excited Feshbach resonance-consistent with observations in simpler alcohols [26,27]. Additionally, we report new fragment anions (C 2 H 2 O -and C 2 H 4 O -) not previously observed. This work establishes a robust framework for interpreting DEA spectra in alcohols, highlighting the critical role of core-excited Feshbach resonances at intermediate energies and providing quantitative cross-section data essential for modeling in radiation science, astrochemistry, and plasma applications.
A time-of-flight (ToF) mass spectrometer was employed in this study. The experimental configuration and operating principles have been described in detail previously [28]; a brief overview is provided here.
A pulsed electron beam is generated using a home-built electron gun based on thermionic emission from a resistively heated tungsten filament. The emitted electrons are shaped and guided by a series of electrodes maintained at appropriate bias potentials. Temporal control is achieved by applying a positive voltage pulse (200 ns duration, 10 kHz repetition rate) to release electrons from a normally blocking potential. The electron gun is enclosed within Helmholtz coils that generate a uniform magnetic field (approximately 40 G) along the beam axis, ensuring collimated propagation. A Faraday cup located downstream measures the time-averaged beam current. Due to instrumental constraints, electron energies below 3.5 eV are not accessible, as electrons fail to reach the interaction region or Faraday cup. All measurements are therefore reported for incident electron energies above 3.5 eV.
The molecular target is introduced as a continuous effusive beam through a 1 mm orifice needle mounted in, but electrically isolated from, the repeller plate. The spectrometer axis is aligned with the molecular beam, which intersects the electron beam at right angles. Electron-molecule collisions occur in the region between repeller and attractor plates, producing negative ions via DEA. Ions are extracted and transported to a microchannel plate (MCP) detector using a three-element einzel lens and a field-free drift tube.
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