Anna Andrejeva

Theoretical study of M(+)-RG2 (M+ = Li, Na, Be, Mg; RG = He-Rn).

Ab initio calculations were employed to determine the geometry (MP2 level), and dissociation energies [MP2 and RCCSD(T) levels], of the M(IIa)(+)-RG2 species, where M(IIa) is a group 2 metal, Be or Mg, and RG is a rare gas (He-Rn). We compare the results with similar calculations on M(Ia)(+)-RG2, where M(Ia) is a group 1 metal, Li or Na. It is found that the complexes involving the group 1 metals are linear (or quasilinear), whereas those involving the group 2 metals are bent. We discuss these results in terms of hybridization and the various interactions in these species. Trends in binding energies, D(e), bond lengths, and bond angles are discussed. We compare the energy required for the removal of a single RG atom from M(+)-RG2 (D(e2)) with that of the dissociation energy of M(+)-RG (D(e1)); some complexes have D(e2) > D(e1), some have D(e2) < D(e1), and some have values that are about the same. We also present relaxed angular cuts through a selection of potential energy surfaces. The trends observed in the geometries and binding energies of these complexes are discussed. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are performed, and it is concluded that the AIM method is the most reliable, giving results that are in line with molecular orbital diagrams and contour plots; unphysical amounts of charge transfer are suggested by the Mulliken and natural population approaches.

Vibrations of the S1 state of fluorobenzene-h5 and fluorobenzene-d5 via resonance-enhanced multiphoton ionization (REMPI) spectroscopy

We report resonance-enhanced multiphoton ionization spectra of the isotopologues fluorobenzene-h5 and fluorobenzene-d5. By making use of quantum chemical calculations, the changes in the wavenumber of the vibrational modes upon deuteration are examined. Additionally, the mixing of vibrational modes both between isotopologues and also between the two electronic states is discussed. The isotopic shifts lead to dramatic changes in the appearance of the spectrum as vibrations shift in and out of Fermi resonance. Assignments of the majority of the fluorobenzene-d5 observed bands are provided, aided by previous results on fluorobenzene-h5.

Assignment of the vibrations of the S0, S1, and D0+ states of perhydrogenated and perdeuterated isotopologues of chlorobenzene

We report vibrationally resolved spectra of the S1←S0 transition of chlorobenzene using resonance-enhanced multiphoton ionization spectroscopy. We study chlorobenzene-h5 as well as its perdeuterated isotopologue, chlorobenzene-d5. Changes in the form of the vibrational modes between the isotopologues and also between the S0 and S1 electronic states are discussed for each species. Vibrational bands are assigned utilizing quantum chemical calculations, previous experimental results, and isotopic shifts, including those between the (35)Cl and (37)Cl isotopologues. Previous work and assignments of the S1 spectra are discussed. Additionally, the vibrations in the ground state cation, D0 (+), are considered, since these have also been used by previous workers in assigning the excited neutral state spectra.

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of bromobenzene and its perdeuterated isotopologue: Assignment of the vibrations of the S0, S1, and D0+ states of bromobenzene and the S0 and D0+ states of iodobenzene

We report vibrationally resolved spectra of the S1←S0 transition of bromobenzene using resonance-enhanced multiphoton ionization spectroscopy. We study bromobenzene-h5 as well as its perdeuterated isotopologue, bromobenzene-d5. The form of the vibrational modes between the isotopologues and also between the S0 and S1 electronic states is discussed for each species, allowing assignment of the bands to be achieved and the activity between states and isotopologues to be established. Vibrational bands are assigned utilizing quantum chemical calculations, previous experimental results, and isotopic shifts. Previous work and assignments of the S1 spectra are discussed. Additionally, the vibrations in the ground state cation, D0 (+), are considered, since these have also been used by previous workers in assigning the excited neutral state spectra. We also examine the vibrations of iodobenzene in the S0 and D0 (+) states and comment on the previous assignments of these. In summary, we have been able to assign the corresponding vibrations across the whole monohalobenzene series of molecules, in the S0, S1, and D0 (+) states, gaining insight into vibrational activity and vibrational couplings.

Theoretical study of M+ RG2: (M+= Ca, Sr, Ba and Ra; RG= He–Rn)

Ab initio calculations were employed to investigate M(+)-RG2 species, where M(+) = Ca, Sr, Ba, and Ra and RG = He-Rn. Geometries have been optimized, and cuts through the potential energy surfaces containing each global minimum have been calculated at the MP2 level of theory, employing triple-ζ quality basis sets. The interaction energies for these complexes were calculated employing the RCCSD(T) level of theory with quadruple-ζ quality basis sets. Trends in binding energies, De, equilibrium bond lengths, Re, and bond angles are discussed and rationalized by analyzing the electronic density. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are presented. It is found that some of these complexes involving the heavier group 2 metals are bent whereas others are linear, deviating from observations for the corresponding Be and Mg metal-containing complexes, which have all previously been found to be bent. The results are discussed in terms of orbital hybridization and the different types of interaction present in these species.

A Surprisingly Simple Electrostatic Model Explains Bent Versus Linear Structures in M+-RG2 Species (M = Group 1 Metal, Li–Fr; RG = Rare Gas, He–Rn)

It is found that a simple electrostatic model involving competition between the attractive dispersive interaction and induced-dipole repulsion between the two RG atoms performs extremely well in rationalizing the M(+)-RG2 geometries, where M = group 1 metal and RG = rare gas. The Li(+)-RG2 and Na(+)-RG2 complexes have previously been found to exhibit quasilinear or linear minimum-energy geometries, with the Na(+)-RG2 complexes having an additional bent local minimum [A. Andrejeva, A. M. Gardner, J. B. Graneek, R. J. Plowright, W. H. Breckenridge, T. G. Wright, J. Phys. Chem. A, 2013, 117, 13578]. In the present work, the geometries for M = K-Fr are found to be bent. A simple electrostatic model explains these conclusions and is able to account almost quantitatively for the binding energy of the second RG atom, as well as the form of the angular potential, for all 36 titular species. Additionally, results of population analyses are presented together with orbital contour plots; combined with the success of the electrostatic model, the expectation that these complexes are all physically bound is confirmed.

Consistent Assignment Of The Vibrations Of Para Disubstituted Benzene Molecules

When disubstituted benzene molecules are considered the relative position of the substituents must be defined. The three possible forms are ortho-, meta-, and parawhere the latter is investigated in this work by consideration of the effect para positioned substituents will have on the vibrational modes. The consistency of the labelling and assignment of the vibrational frequencies of the para disubstituted benzene molecules is investigated in their ground states (S0) and first electronically excited states (S1). The work extends a previously published nomenclature where ring-localised vibrations are compared straightforwardly across different monosubstituted benzene species and given the label Mi. The assignments of the frequencies include previous work but also the calculated wavenumbers for both hydrogenated disubstituted benzenes (-h4) and the deuterated isotopologues (-d4) employing density functional theory (DFT) and time-dependent density functional theory (TDDFT).