Same but Different: Dipole-Stabilized Shape Resonances in CuF^– and AgF^–

Abstract

Electron attachment to closed-shell molecules is a gateway to various important processes in the gas and condensed phases. The properties of an electron-attached state, such as its energy and lifetime as well as the character of the molecular orbital to which the electron is attached, determine the fate of the anion. In this experimental and theoretical study of copper and silver fluoride anions, we introduce a new type of metastable anionic state. Abrupt changes in photoelectron angular distributions point to the existence of autodetaching states. Equation-of-motion coupled-cluster singles and doubles calculations augmented by a complex absorbing potential identify some of these states as Σ and Π dipole-stabilized resonances, a new type of shape resonance. In addition, these molecules support valence and dipole-bound states and a Σ resonance of charge-transfer character. By featuring five different types of anionic states, they provide a vehicle for studying fundamental properties of anions and for validating new theoretical approaches for metastable states.

Multireference perturbation theory with improved virtual orbitals for radicals: More degeneracies, more problems

“…Concerning o-benzyne, Mk-MRCCSD method suggests the C1 C2 distance to be about 0.15 Å longer in the lowest triplet state than in the singlet ground state, whereas for p-benzyne the C1 C4 bond length reduces by about 0.07 Å in the triplet state compared to the ground state. [85] For the o-and p-benzynes, the IVO-SSMRPT method's geometrical data predictions agree most closely with that of the CR-CC, CCSD(T), and p2-RDM (parametric two-electron reduced-density matrix) level of formalisms. [89] For obenzyne system, the distance between the radical centers is suggested to be 1.267, 1.273, 1.260, and 1.277 Å by the CCSD, CR-CC, CCSD(T), and p2-RDM (two-electron reduced-density matrix) approaches, respectively.…”

“…As depicted in the error. Note that the Mk-MRCCSD(2,2)/cc-pCVTZ [85] overestimates the S-T splitting by nearly 0.9 kcal/mol for o-benzyne. We also observe a satisfactory agreement of our results with the EOM-SF-based CCSD and CCSD(T) calculations for ΔE ST gaps.…”

“…For p-benzyne, the CCSD, EOMEE-CCSD, RMR CCSD, and CR-CC(2,3) level of computations suggest the triplet be the ground state which is certainly not the experimental fact. [84,85] This finding also speaks in favor of employing MR-based methods to the electronic states of diradicals. In the case of From Table 3, one may observe that IVO-SSMRPT ST splitting is also in near-perfect agreement with the results computed with the largest active space-based driven similarity renormalization group second-order multireference perturbation theory (DSRG-MRPT2) with cc-pVDZ basis set.…”

“…Benzynes [such as o and p-benzynes] are probably the most investigated systems among the aromatic σ, σ biradicals both by numerous manybody theories [77][78][79][80][81][82][83][84][85][86][87] and experiments. [88] p-Benzyne is indeed infamous for its computational challenges.…”

“…We also found that our S-T splittings estimated at the IVO-SSMRPT(2,2)/cc-pVTZ level of theory agree within 2 kcal/mol for o-benzyne and 0.9 kcal/mol for p-benzyne with the values determined at the Mk-MRCCSD(2,2)/cc-pCVTZ level of calculations (38.62 kcal/mol for o-benzyne and 4.86 kcal/mol for p-benzyne). [85] In an extensive study, Li and coworkers [82] performed block-correlated coupled cluster (BCCC) theory with a CASSCF(2,2) reference function calculations on three benzyne isomers for ST gaps. Their observations are also in good agreement with our IVO-SSMRPT(2,2) conclusion.…”