Distinction of photoelectron spectroscopy of cis- and trans-acrolein explored by theoretical computation

Abstract

• The photoelectron spectra for the two lowest cationic states of cis - and trans -acrolein have been simulated. • Trans -acrolein is identified as the primary isomer responsible for the experimental photoelectron spectra. • The cis -acrolein anion is calculated to be more stable than the trans form, contrary to acrolein molecules. • The barrier for trans - cis isomerization of acrolein anion is high, and which isomer of acrolein anion will be produced is unknown We calculated the equilibrium structures and harmonic vibrational frequencies of acrolein (including molecule, cation and anion) using the B3LYP, PBE0, and M06-2X approaches. We also computed the Franck–Condon factors and simulated the photoelectron spectra of acrolein molecules and anions. The adiabatic ionization energy (AIE) and electron affinity were computed using the CCSD(T) approach via extrapolation to the complete basis set limit. Trans -acrolein is identified as the primary isomer responsible for the photoelectron spectra of acrolein being observed. The calculated AIEs were consistent with the experiment. The cis -acrolein anion is predicted to be more stable than its trans- counterpart. However, the potential barrier might prohibit the isomerization of the acrolein anion. Accordingly, the type of isomer of acrolein anion that will be produced from electron-attaching to the more stable trans -acrolein molecule remains unknown. The simulated photoelectron spectra of the acrolein anion can be used to identify the isomer being produced.