The OH+cation is a well‐known diatomic for which the triplet (3Σ−) ground state is 50.5 kcal mol−1more stable than its corresponding singlet (1Δ) excited state. However, the singlet forms a strong donor–acceptor bond to argon with a bond energy of 66.4 kcal mol−1at the CCSDT(Q)/CBS level, making the singlet ArOH+cation 3.9 kcal mol−1more stable than the lowest energy triplet complex. Both singlet and triplet isomers of this molecular ion were prepared in a cold molecular beam using different ion sources. Infrared photodissociation spectroscopy in combination with messenger atom tagging shows that the two spin isomers exhibit completely different spectral signatures. The ground state of ArOH+is the predicted singlet with a covalent Ar−O bond.
We recently proposed a semi-stochastic approach to converging high-level coupled-cluster (CC) energetics, such as those obtained in the CC calculations with singles, doubles, and triples (CCSDT), in which the deterministic CC(P;Q) framework is merged with the stochastic configuration interaction Quantum Monte Carlo propagations [J. E. Deustua, J. Shen, and P. Piecuch, Phys. Rev. Lett. 119, 223003 (2017)]. In this work, we investigate the ability of the semi-stochastic CC(P;Q) methodology to recover the CCSDT energies of the lowest singlet and triplet states and the corresponding singlet–triplet gaps of biradical systems using methylene, (HFH)−, cyclobutadiene, cyclopentadienyl cation, and trimethylenemethane as examples.
more » « less- Award ID(s):
- 1763371
- NSF-PAR ID:
- 10440304
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 157
- Issue:
- 13
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract The OH+cation is a well‐known diatomic for which the triplet (3Σ−) ground state is 50.5 kcal mol−1more stable than its corresponding singlet (1Δ) excited state. However, the singlet forms a strong donor–acceptor bond to argon with a bond energy of 66.4 kcal mol−1at the CCSDT(Q)/CBS level, making the singlet ArOH+cation 3.9 kcal mol−1more stable than the lowest energy triplet complex. Both singlet and triplet isomers of this molecular ion were prepared in a cold molecular beam using different ion sources. Infrared photodissociation spectroscopy in combination with messenger atom tagging shows that the two spin isomers exhibit completely different spectral signatures. The ground state of ArOH+is the predicted singlet with a covalent Ar−O bond.
-
null (Ed.)A novel pyranine derivative, Et HPTA-OH, was synthesized via the substitution of the anionic sulfonate groups with neutral diethylsulfonamide groups. The photophysical and photochemical properties of Et HPTA-OH were studied using photoluminescence quenching and transient absorption spectroscopy. The singlet state of Et HPTA-OH was found to be highly photoacidic (p K a * = 8.74 in acetonitrile). A series of aniline and pyridine bases were used to investigate excited-state proton transfer (ESPT) from singlet Et HPTA-OH, and rate constants for singlet quenching via ESPT were determined ( k q = 5.18 × 10 9 to 1.05 × 10 10 M −1 s −1 ). Et HPTA-OH was also found to exhibit a long-lived triplet state which reacts through a triplet–triplet annihilation (TTA) process to reform singlet Et HPTA-OH on timescales of up to 80 μs. Detection of ESPT photoproducts on timescales comparable to that of TTA singlet regeneration provides strong evidence for photoacidic behavior stemming from the regenerated singlet Et HPTA-OH.more » « less
-
We report results from experiments with the quinoline-O2 complex, which was photodissociated using light near 312 nm. Photodissociation resulted in formation of the lowest excited state of oxygen, O2 a 1Δg, which we detected using resonance enhanced multiphoton ionization and velocity map ion imaging. The O2+ ion image allowed for a determination of the center-of-mass translational energy distribution, P(ET), following complex dissociation. We also report results of electronic structure calculations for the quinoline singlet ground state and lowest energy triplet state. From the CCSD/aug-cc-pVDZ//(U)MP2/cc-pVDZ calculations, we determined the lowest energy triplet state to have ππ* electronic character and to be 2.69 eV above the ground state. We also used electronic structure calculations to determine the geometry and binding energy for several quinoline-O2 complexes. The calculations indicated that the most strongly bound complex has a well depth of about 0.11 eV and places the O2 moiety above and approximately parallel to the quinoline ring system. By comparing the experimental P(ET) with the energy for the singlet ground state and the lowest energy triplet state, we concluded that the quinoline product was formed in the lowest energy triplet state. Finally, we found the experimental P(ET) to be in agreement with a Prior translational energy distribution, which suggests a statistical dissociation for the complex.more » « less
-
more » « less
Abstract The chemical stability and the low‐lying singlet and triplet excited states of BN‐
n ‐acenes (n = 1–7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet‐triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon‐only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet‐triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN‐n ‐acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low‐lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron.
