We report on an experimental and theoretical investigation of the ground electronic potential of dicopper. By taking into account our recent deperturbation study of the high lying energy map,Beck, M., P. Bornhauser, Bradley Visser, G. Knopp, J. A. van Bokhoven, and P. P. Radi. Nature Communications, 10(2019)3270ateway levels are identified that allow access to vibrational levels of the ground state up to ≈ 98% of the dissociation limit. Rotationally resolved two-color resonant four-wave mixing spectra (TC-RFWM) are analyzed by applying the 'near-dissociation expansion' (NDE) introduced by Le Roy.Le Roy, Robert J. Journal of Quantitative Spectroscopy and Radiative Transfer, 186(2017)197n addition to the determination of D_e, an accurate potential energy function is obtained to assess the structural and dynamical properties of this important transition metal species. Ab initio computations at the multi-reference configuration-interaction level of theory shed further light on the bound characteristics of this diatomic molecule.

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Beck, M., P. Bornhauser, Bradley Visser, G. Knopp, J. A. van Bokhoven, and P. P. Radi. Nature Communications, 10(2019)3270g Le Roy, Robert J. Journal of Quantitative Spectroscopy and Radiative Transfer, 186(2017)197I

The B̃ ²E′ - X̃ ²A₂′ system of jet cooled NO₃ is investigated via laser induced fluorescence ( LIF ). Dispersed fluorescence ( DF ) spectra from single vibronic levels of the upper electronic state have been measured. It has been reported that the vibronic bands observed in the red absorption spectrum of the B̃ - X̃ system have broadened characteristicsD. A. Ramsay, in Proceedings of the Tenth Colloquium Spectroscopicum Internationale, edited by E. R. Lippencott and M. Margoshes (Spartan Books, Washington, DC., 1963), p. 593-596. The vibrational structure of the DF spectrum obtained by excitation of the 0+770 cm⁻¹ band shows several fluorescence bands terminated to the out-of-plane vibrational levels in the lower X̃ ²A₂′ state, such as a₂" and e", e.g. the fluorescence band emitting to the e" level of ν₂ + ν₄. The present observation indicates that the fluorescent vibronic level lying 770 cm⁻¹ above the vibrationless level of the B̃ ²E′ state has contributions of the ν₂ and ν₄ modes and/or that the fluorescent level has an out-of-plane geometry. It is concluded that, because the fundamental and over-tone bands of the ν₂ and ν₄ modes, respectively, in the X̃ ²A₂′ state lie  ∼  760 cm⁻¹R. R. Friedl and S. P. Sander, J. Phys. Chem. 91, 2721 (1987)K. Kawaguchi et al., J. Mol. Spectrosc. 334, 10 (2017), the 0+770 cm⁻¹ level is attributed the level coupled by the ν₂ fundamental and 2ν₄ over-tone levels. This also suggests that the out-of-plane vibrational levels are important to analyze the vibrational structure of the X̃ ²A₂′ state.

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Footnotes:

D. A. Ramsay, in Proceedings of the Tenth Colloquium Spectroscopicum Internationale, edited by E. R. Lippencott and M. Margoshes (Spartan Books, Washington, DC., 1963), p. 593-596.. R. R. Friedl and S. P. Sander, J. Phys. Chem. 91, 2721 (1987)

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Alkali earth metal dimers, specifically Ca₂, are of theoretical interest [1,2] due to their weakly bound X¹Σ_g ground state, arising from a fully occupied anti-bonding σ_u molecular orbital. Experimentally, alkali earth metals are of interest for ultra-cold chemical and physics applications. Due to their similar electronic structure to that of alkali metal atoms, alkali earth metal ions can be laser-cooled and readily formed in Coulomb crystals[3,4]. By inducing reactions, molecular ions can be generated within the Coulomb crystal, where they are translationally cooled by the surrounding atomic ions. Photodissociation techniques can then be used to detect the molecular ions via depletion. In the case of Ca₂⁺, there are few available spectroscopic data that can be used to determine the frequencies of vibronic transitions that could be intermediates for photodissociation spectroscopy. To obtain such information, the neutral Ca₂ dimer should be spectroscopically characterized in greater detail. Previous spectroscopic efforts have observed vibronic emissions from the strongly perturbed A¹Σ_u and B¹Σ_u states to the ground state[1]. In this work, Ca₂ was created through laser ablation and supersonic expansion techniques, jet-cooled to 4K. Using an excimer-pumped dye laser, resonant and dispersed laser-induced fluorescence (LIF, DLIF) were performed. Dispersed LIF was detected by sending the fluorescence through a monochromator and detecting dispersed fluorescence with a photomultiplier tube (PMT). Lifetimes of emitting states were also measured. For the first time, the c³Π_u-X¹Σ_g vibronic transitions of Ca₂ were experimentally observed. Using DLIF, vibrational sequences in the X¹Σ_g state were observed, confirming X¹Σ_g as the emission’s lower state. [1] Bondybey, V. et al. Chem. Phys. Lett. 1984, 111, 195 [2] Allard, O. et al. Eur. Phys. J. D 2005, 35, 483 [3] Nguyen, J. et al. New. J. Phys. 2011, 13, 063023 [4] Calvin, A. et al. J. Phys. Chem. Lett. 2018, 9, 5797

Polyaromatic hydrocarbon (PAH) anions are proposed to be present in the interstellar medium. These molecules, which do not feature a large enough dipole moment to capture an electron via a dipole-bound state, are instead purported to capture electrons via broad π-resonances. These π-resonances are closely spaced anion excited electonic states. We use an action spectroscopy that monitors total photoelectron yield of these anions above detachment threshold. This investigates the many states present in the dense manifold of electronic states. With the resolution of our instrument, we are able to deconvolute these π-resonances. In addition, we report new electron affinity values for isomers of tetracenyl radical using high resolution photoelectron spectroscopy. One radical in particular, 9-tetracenyl, EA = 1.845eV, disagrees with the previous literature value, 2.6eV.

In this project, we have studied the electronic structure of RhO²⁺ using high level quantum mechanical calculations. Multireference method (MRCI) has been employed in combination with large basis sets to construct the potential energy profiles of the ground and excited states of RhO²⁺ with different spin multiplicities. Spectroscopic constants have been tabulated for 20 states along with the spin-orbit calculation for a few low-lying states. The ground state of RhO²⁺ is ²Π followed by ⁴∆ and ²∆. The equilibrium bond lengths for these states are between 1.594-1.752 Å and the electronic structure is in situ Rh⁴⁺O²⁻ that corresponds to an oxo moiety. The next state is ⁶Σ⁺ with an equilibrium bond length of 2.161 Å and possesses an in situ electronic structure of Rh³⁺O⁻ that corresponds to oxyl character with one unpaired electron on oxygen. Further investigation reveals that ⁶Σ⁺, which is 19.6 kcal/mol higher in energy than the ²Π (ground state), has the potency to activate C-H bond of methane with higher efficiency. Finally, from the spin-orbit calculations, the ground state of RhO²⁺ is assigned ²Π_1/2 followed by the state ⁴∆_7/2. In future, this project is going to probe the effect of ligands in the electronic structure of RhO²⁺.

Using ILS-FTS, we have recorded the A Ω=1 – X Ω=0⁺ transition of diatomic PtS. Strong bands were observed at 15,520 and 15,910 cm⁻¹, which have been identified as the (0,0) and (1,0) vibrational bands. The P- and R-branches show a regular pattern for the ¹⁹⁴PtS, ¹⁹⁵PtS, ¹⁹⁶PtS and ¹⁹⁸PtS isotopologues, but quite interestingly the Q-branch shows significant hyperfine splitting for ¹⁹⁵PtS. Although P- and R-branches were easily assigned based on the known ground state constants, the Q-branch seems to be perturbed, requiring q, q_D, and q_H parameters to achieve only a sub-par fit. This indicates the presence of a nearby Ω=0⁻ state that is perturbing the f–levels in the A Ω=1 state. A successful deperturbation analysis and fit were performed in PGOPHER, and molecular constants for the A Ω=1 and perturbing Ω=0⁻ states were obtained. High-level ab initio calculations support this assignment and predict an Ω=0⁻ state in close proximity to the A state. Results and discussion of this analysis will be presented.

Heteronuclear diatomic molecules consisting of alkaline and alkaline-earth metals, such as LiMg have properties that make them potentially useful for ultra-cold molecule experiments. The X²Σ⁺ ground state of LiMg allows it to be manipulated by both magnetic and electric fields, and its non-zero dipole moment offers the possibility that it could be used in quantum computing devices. Current spectroscopic data for the excited states of LiMg are limited, consisting of a few vibrationally resolved bands of E-X and F-X systems¹. Bound-free emission spectra have been attributed to the D-X and C-X transitions². In the present study we have used resonantly enhanced two-photon ionization spectroscopy and laser induced fluorescence measurements to record rotationally resolved spectra for the E-X and F-X bands. Transitions to bound levels of the D state are reported for the first time. The ionization threshold for LiMg will be determined using photoionization efficiency spectroscopy. 1. Berry, K.R. and Duncan, M.A., (1997) Photoionization spectroscopy of LiMg. Chem. Phys. Lett., 279, 44-49 2. Pichler, G., Lyyra, A.M., Kleiber, P.D., Stwalley, W.C., Hammer, R., Sando, K.M., and Michels, H.H., (1989) Laser-induced chemiluminescence of the lithium-magnesium (LiMg) excimer. Chem. Phys. Lett., 156, 467-71

Despite the fact that diatomic alkaline earth monoxides are deeply bound, closed shell molecules, hypermetallic species of the form MOM are also found to be stable. Formally these molecules have ionic bonds of the form M⁺O²⁻M⁺. Each M⁺ ion hosts an unpaired electron, and the interactions between these well separated electrons are weak. As a consequence the singlet-triplet energy interval is small, and the lowest energy singlet state is strongly multi-reference in character. In the present study we have characterized MgOMg by means of laser induced fluorescence and resonantly enhanced multi-photon ionization (REMPI) spectroscopy. Rotationally resolved electronic spectra have been recorded for multiple bands of the A¹A₁ – X¹Σ⁺_g transition in the range of 21500 – 23000 cm⁻¹. The spectra were consistent with bent and linear equilibrium structures for the excited and ground states. Fluorescence decay lifetimes were found to be 39±1 ns, and the ground state vibrational structure was examined by means of dispersed fluorescence spectroscopy. The attribution of the observed excitation bands to MgOMg was confirmed by recording REMPI spectra with mass-resolved ion detection. Two-color ionization measurements defined an ionization energy of 53515 cm⁻¹, close to a computational prediction of 53330 cm⁻¹.

The chemical evolution in photon-dominated regions (PDRs), including some diffuse interstellar clouds and protoplanetary disks, is closely related to photochemistry triggered by vacuum ultraviolet (VUV) photons, which act as the most important source of energy in such astronomical enviroments. Though the photodissociation and photoionization of transient diatomic C-bearing molecules play an important role in the chemical network of carbon in space, a lack of laboratory studies and theoretical calculations of their high-lying excited states impedes accurate modeling of their photochemistry and interpretation of astronomical observations. We have investigated the photochemistry of two molecules CS and in the VUV region. Experimentally, the molecules are generated by photolysis or discharge of corresponding precursors and then supersonically expanded into a vacuum chamber, where they are interrogated by state-selective VUV-VUV spectroscopy coupled with velocity map imaging. In combination with new accurate ab initio calculations, our study contributes quantitative data for use in photochemical databases.

With recent interest in quantum simulations as well as technologies such as spintronics and magnetic materials, the importance of electron correlation has been ever increasing. Lanthanide oxides, with their close lying electronic states stemming from the presence of 4f electrons, have been of immense interest in recent years as a result. Developing the breadth of knowledge of these materials is necessary and can help reveal the patterns in the impact of lanthanide identity on the electron correlation. Previous studies conducting anion photoelectron spectroscopy on small lanthanide oxide clusters have indicated strong interactions between departing photoelectron and valence electrons of the neutral cluster, shown by an increase in excited state band intensity with a decrease in photon energy, opposite of that predicted by the threshold law. To better understand this relationship between the electron correlation and the interactions between the photoelectron and the neutral core and its change with lanthanide identity, the anion photoelectron spectra of Ce₃O, Sm₃O, and Gd₃O were collected at 2.330 eV and 3.495 eV.