Formation of Hydroxyl Anion via a 2-Particle 1-Hole Feshbach Resonance in DEA to 2-Propanol: A Joint Experimental and Theoretical Study

Abstract

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.

Figures (6)

• Figure 1: Mass spectrum from DEA to 2-propanol at $8.2\,\mathrm{eV}$ electron energy, showing four fragment anions: OH^- (17 amu), C2H2O^- (42 amu), C2H4O^- (44 amu), and C3H7O^- (59 amu). The ToF channel number is indicated above. The ToF-to-$m/q$ calibration is performed using DEA mass spectra of SO$_2$ at an incident electron energy of 4.5 eV.
• Figure 2: Ion yields for fragment anions from DEA to 2-propanol as functions of electron energy (3.5--13 eV). (a) $\mathrm{OH^-}$ (17 amu) shows a prominent resonance at 8.2 eV; Absolute cross section for $\mathrm{OH^-}$ formation from 2-propanol via DEA, where the resonance peak was obtained from a Gaussian fit with constant background to the experimental data, yielding a maximum cross section of $4.188 \times 10^{-19}$ cm$^2$ at 8.2 eV. (b) $\mathrm{C_2H_2O^-}$ (42 amu) exhibits a broad feature; (c) $\mathrm{C_2H_4O^-}$ (44 amu) shows multiple resonances; (d) $\mathrm{C_3H_7O^-}$ (59 amu) displays a distinct resonance profile.
• Figure 3: Potential energy curves for the ground ($\tilde{X}$) and electron-attached excited ($\tilde{S}$) resonance states of 2-propanal (C$_s$ symmetry) along the C-OH bond dissociation coordinate. The curves represent the resonance energies as a function of the C--OH bond distance, obtained from electron-attached equation-of-motion coupled-cluster calculations. The magenta-dashed vertical lines indicate the Franck-Condon region (1.45--1.55 Å) relevant to vertical electron attachment. Among these electron-attached resonance states, only the purely repulsive states with sufficiently narrow resonance widths contribute significantly to the formation of OH$^-$ fragments through dissociative electron attachment via 2-particle 1-hole Feshbach resonances. The downward red arrow marks the kinetic energy carried by the OH$^-$ product after the DEA.
• Figure 4: Complex energy plane showing resonance trajectories (smoothed). The $\mathrm{Im}(E)$ vs. $\mathrm{Re}(E)$ plot highlights the resonance positions and widths.
• Figure 5: (Left) Normalized survival probability versus resonance energy, showing Feshbach resonances (red stars) with $\Gamma < 0.25$ eV. (Right) Log--log plot of survival probability versus resonance width, confirming exponential decay behavior. The slopes yield the decay widths $\Gamma$, with narrow-width resonances ($\Gamma < 0.25$ eV) having appreciable survival probabilities.