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We report a combined experimental and theoretical investigation of electron scattering from nitrous oxide (N2O). Experimental two-dimensional electron energy loss spectra (EELS) provide information about vibrational states of a molecule and about potential energy surfaces of anionic resonances. This study reports the EELS measured at 2.5–2.6 eV incident energy. The calculations using complex-valued extensions of equation-of-motion coupled-cluster theory (based on the non-Hermitian quantum mechanics) facilitate the assignment of all major EELS features. Our simulations identified two broad and partially overlapping resonances—one of π* and another of σ* character—located at ∼2.8 and 2.3 eV vertically at the equilibrium geometry of the neutral. Due to the Renner–Teller effect, the π* resonance splits upon bending. The upper state, 2Π, remains linear. The lower state mixes with the σ* configuration, giving rise to the 2A′ resonance, which becomes strongly stabilized at bent geometries (αNNO = 134°), resulting in very low adiabatic electron attachment energy. The calculations estimate the electron affinity of N2O to be −0.140 eV. The 2A′ state is predissociative, with the barrier for the N–O bond dissociation of 0.183 eV. The measured EELS feature sharp vibrational structures at low energy losses, followed by a linear (in logarithmic scale) tail extending to the maximum energy loss. The simulations attribute the sharp features at the low energy loss to the non-resonant excitations and contributions from the cold 2Π resonance. The tail is attributed to the vibrationally hot 2A′ state, and its slope is determined by the excess energy available in this state. 

We investigate attachment of slow electrons (0–10 eV) to naphthalene (Np) clusters in a crossed beam experiment. Supersonic expansions under different conditions using different buffer gases generate the clusters: in He, Ne, and low pressure Ar, neat (Np)N clusters are formed, while we also observe mixed clusters of naphthalene with rare-gas atoms in co-expansion with Ar above 0.5 bar and with Kr. Negatively charged (Np)n− and Rgm(Np)n− (Rg = Ar, Kr) clusters are analyzed by mass spectrometry, and electron energy dependent ion yields are measured. We show that the smallest stable naphthalene complex with an excess electron, the dimer (Np)2− anion, cannot be formed in a binary collision of a free electron with (Np)2 dimer, nor with (Np)3 trimer. Evaporation of a weakly bound Ar atom(s) from a mixed ArM(Np)2 cluster following electron attachment leads to the dimer (Np)2− anion. Larger (Np)n−, n > 3, transient cluster anions decay via evaporation of an Np unit on a timescale of tens of microseconds. The self-scavenging process opens around 6 eV, where a naphthalene unit is electronically excited by the incoming electron, which is slowed down and trapped. However, the transient negative ion is efficiently stabilized only in the mixed clusters, from which Ar atom(s) can be evaporated. 

We probe the separation of ligands from iron tetracarbonyl methyl acrylate (Fe(CO)₄(C₄H₆O₂) or Fe(CO)₄MA) induced by the interaction with free electrons. The motivation comes from the possible use of this molecule as a nanofabrication precursor and from the corresponding need to understand its elementary reactions fundamental to the electron-induced deposition. We utilize two complementary electron collision setups and support the interpretation of data by quantum chemical calculations. This way, both the dissociative ionization and dissociative electron attachment fragmentation channels are characterized. Considerable differences in the degree of precursor fragmentation in these two channels are observed. Interesting differences also appear when this precursor is compared to structurally similar iron pentacarbonyl. The present findings shed light on the recent electron-induced chemistry of Fe(CO)₄MA on a surface under ultrahigh vacuum. 

We report a combined experimental and theoretical investigation of electron–molecule interactions using pyrrole as a model system. Experimental two-dimensional electron energy loss spectra (EELS) encode information about the vibrational states of the molecule as well as the position and structure of electronic resonances. The calculations using complex-valued extensions of equation-of-motion coupled-cluster theory (based on non-Hermitian quantum mechanics) facilitate the assignment of all major EELS features. We confirm the two previously described π resonances at about 2.5 and 3.5 eV (the calculations place these two states at 2.92 and 3.53 eV vertically and 2.63 and 3.27 eV adiabatically). The calculations also predict a low-lying resonance at 0.46 eV, which has a mixed character—of a dipole-bound state and σ* type. This resonance becomes stabilized at one quanta of the NH excitation, giving rise to the sharp feature at 0.9 eV in the corresponding EELS. Calculations of Franck–Condon factors explain the observed variations in the vibrational excitation patterns. The ability of theory to describe EELS provides a concrete illustration of the utility of non-Hermitian quantum chemistry, which extends such important concepts as potential energy surfaces and molecular orbitals to states embedded in the continuum. 

In a combined experimental and theoretical study we probe the transient anion states (resonances) in cyanogen. Experimentally, we utilize electron energy loss spectroscopy which reveals the resonance positions by monitoring the excitation functions for vibrationally inelastic electron scattering. Four resonances are visible in the spectra, centered around 0.36 eV, 4.1, 5.3 and 7.3 eV. Theoretically, we explore the resonant states by using the regularized analytical continuation method. A very good agreement with the experiment is obtained for low-lying resonances, however, the computational method becomes unstable for higher-lying states. The lowest shape resonance ( 2 Π u ) is independently explored by the complex adsorbing potential method. In the experiment, this resonance is manifested by a pronounced boomerang structure. We show that the naive picture of viewing NCCN as a pseudodihalogen and focusing only on the CC stretch is invalid.