Due to their higher melting point and metal ion density compared to their oxide counterparts, actinide nitrides are promising candidates for nuclear fission sources in nuclear reactors. While thorium mononitride (ThN) is a possible fission source in thorium-based reactors, few studies on ThN have been conducted. Previous ThN studies have characterized gas-phase rovibronic transitions through resonance-enhanced multiphoton ionization (REMPI) and laser-induced fluorescence (LIF) spectroscopic methods[1]. These uncalibrated low-resolution survey spectra, however, were mostly unanalyzed. A calibrated, higher resolution spectrum was recorded for one vibronic band ([20.9]1.5-X²Σ⁺) and spectroscopic constants were reported for the ground state and the electronically excited state[1]. More recently, a second band ([18.0]1.5-X²Σ⁺) has been observed at high-resolution and used to examine the fine and hyperfine structure of ThN(X)[2]. In the present study, ThN was jet-cooled to approximately 100K and LIF spectra were recorded over the range 20,000-21,300 cm⁻¹. A tellurium (Te₂) cell was heated to 650^° C and its absorbance spectrum was used for spectral calibration. Data and analyses of the observed ground state and excited states of ThN will be presented. [1] M.C. Heaven, B.J. Barker, I.O. Antonov, J. Phys. Chem. A, 118 (2014) 10867-10881. [2] A. T. Le, S. Nakhate, T. Nguyen, T. C. Steimle, M. C. Heaven, J. Chem. Phys., submitted

We present our work on a new semi-empirical potential energy surface (PES) for the ground electronic state of the main water isotopologue that provides accurate energy levels up to 37 000 cm⁻¹. A previous attempt (Polyansky et al. (2018)) to model the highly energetic levels has seen two independent potentials being merged together into one, however, to date, it is the only PES available that can provide the necessary wave-functions needed to compute theoretical intensities in the visible and near UV. The purpose of this work is to quantify the error associated with the underlying PES for visible near UV line intensities. An initial ab initio PES has been fitted to 16 170 aug-cc-pCV6Z DKH2 MR-CI data points with a functional form utilizing only 251 parameters. So far, it has been refined to over 3 500 energy levels originating from both MARVEL (Furtenbacher et al. (2007)) and experiment which include rotational levels 0, 1, 2, 3, 4 and 5. Approximately 99% of all possible energy levels have been included in the refining process. The RMS deviation for all levels is currently 0.08 cm⁻¹. It is generally understood that the dipole moment surface (DMS) provides the largest uncertainty to computed intensities, however our results indicate that the error associated with the PES is not negligible, even for the fundamental bands where it can rise to 1%. That number is some times higher for other bands. This becomes significant in interpreting the atmospheric spectra where the quality of the modern spectrometers places high demands on the accuracy of reference spectroscopic data. Through comparisons with the latest available experiments and observations we provide an analysis on the sensitivity of line intensities from the infrared to the near UV.

Wavelength-dependent photodissociation cross sections are key data required by modern astrochemical models to simulate the evolution of chemical species in photon-dominated regions. Although photodissociation is considered as the dominant destruction pathway for carbon monosulfide (CS) in these enviroments, the photodissociation rate pf CS is essentially unknown due to a lack of vacuum ultraviolet (VUV) laboratory measurements and accurate theoretical calculations. Here we present a high-level ab initio study of CS photodissociation, including for the first time a detailed investigation of its predissociation via the B ¹Σ⁺ and C ¹Σ⁺ states. Potential energy curves of CS electronic states were calculated at the MRCI+Q/aug-cc-pV(5+C)Z level and photodissociation cross sections from the vibrational and electronic ground state were calculated by solving the coupled-channel Schrödinger equation. We found that the C−X (0−0) transition followed by spin-orbit coupling into several triplet states is responsible for 73% of the overall photodissociation of CS under the standard interstellar radiation field (ISRF), giving rise to the main atomic products C (³P) and S (¹D). Our new calculations of the photodissociation rate are a factor of 2.4 larger than the value currently adopted by the Leiden database, suggesting that this value may be revised for improving the accuracy of astrochemical models.

High level computational thermochemical protocols take an additive approach to computing the total energy of a molecular system. For small systems, components related to the electronic structure can be systematically converged using methods such as coupled-cluster theory at the complete basis limit. The vibrational level pattern (and at 0 K the zero-point energy, ZPE) yields a relatively large contribution and is thus a possible source of significant error. An inaccurate ZPE leads to poor quantities such as enthalpies of formation and hence interpretations in kinetics and dynamics. As a result an accurate determination of this one term is critical and the focus of this talk. Accurate anharmonic models such as VPT2 and VCI exist for semi-rigid molecules in the gas phase. Non-covalent systems are also of importance in a wide range of areas. The VPT2 model has not been applied as widely to non-covalent systems and questions remain as to its general applicability. Here, a screening of low-cost implementations of VPT2 calculations were performed for a series of vdW systems as large as Benzene-Ar. The screening was done with an automated thermochemical protocol. Comparisons are made with full-dimensional variational calculations using global potential energy surfaces, and to experimental data where available.

Bucky bowl is the molecule of nonplanar polycyclic aromatic hydrocarbons. We analyzed the vibronic sructure in the S₁ ← S₀ fluorescence excitation spectra of jet-cooled sumanene and corannulene. The spectrum is congested with a large number of vibronic bands, which are mostly assigned to out-of-plane vibrational modes. The S₁ state of corannulene is identified to ¹E₂ by the normal mode analysis, which is consistent with the result of SAC-CI calculation. The excitation energy of ¹A₂ state was lower than that of the ¹E₂ state by the TD-DFT method. The isolated corannulene molecule is considered to be a normal pentagon with considerable out-of-plane distortion (C_5v). We observed the IR spectrum of corannulene in solid para-H₂, which also indicates that the moelcule has a structure with five-fold symmetry in the S₀ state. We found the IR bands originated from protonated corannulene molecules, which are produced by the chemical reaction with a proton.
[1] P. Sundararajan, M. Tsuge, M. Baba, and Y.-P. Lee, ACS Earth Space Chem. 2, 1001 (2018)
[2] S. Kunishige, M. Baba, H. Sakurai, et al., J. Chem. Phys. 139, 044313 (2013)

Rotationally-resolved high-resolution fluorescence excitation spectra of the S₁ ← S₀ electronic transition of fluorene and carbazole have been observed. Sub-Doppler excitation spectra were measured by crossing a single-mode UV laser beam perpendicular to a collimated molecular beam. The absolute wavenumber was calibrated with accuracy 0.0002 cm⁻¹ by measurement of the Doppler-free saturation spectrum of iodine molecule and fringe pattern of the stabilized etalon. For fluorene, 7 bands were observed and analyzed from the 0⁰₀ to 0⁰₀+1228 cm⁻¹ band, and their molecular constants were determined with high accuracy. For carbazole, 3 bands were observedand analyzed from the 0⁰₀ to 0⁰₀+1122 cm⁻¹ band, and their molecular constants were also determined. Yi et. al. J. T. Yi, L. Alvarez-Valtierra, and D. W. Pratt, J. Chem. Phys., 124, 244302 (2006).ere reported the lower vibronic bands for both molecules, and their molecular constants are good agreement with the obtained ones except the 0⁰₀+204 cm⁻¹ band of fluorene. We found a typical local energy shift in this 0⁰₀+204 cm⁻¹ band, and it was identified as originating from the perturbation between the vibronic levels in the S₁ state. The Zeeman effect were also observed up to 1.2 T for the 0⁰₀ bands to consider the excited state dynamics.

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J. T. Yi, L. Alvarez-Valtierra, and D. W. Pratt, J. Chem. Phys., 124, 244302 (2006).w

We have assigned spectral species of a LIF spectrum with ¹Π - ¹Σ rotational structure to SiOSi with the aid of ab initio quantum chemical calculationsM. Fukushima and T. Ishiwata, 73rd ISMS, paper MJ09 (2018). Due to the spectrum's red-shaded structure, the R-branch forms a band head, and an analysis adopting the P- and Q-branches had not been satisfactory. As the ab initio calculations suggest the ground electronic state is 1¹Σ_g⁺, we attempted a more precise analysis via combination differences and noted heavy irregularities exclusive to the upper levels of the Q-branch. Considering parities of the rotational levels of the upper Π electronic state, we are investigating this irregularity with the aid of computation.

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Footnotes:

M. Fukushima and T. Ishiwata, 73rd ISMS, paper MJ09 (2018)..

In recent years, derivatives of the 1,4 dihydrobenzo[e][1,2,4]triazin-4-yl radical (e.g. the Blatter1 radical Blatter, H. M.; Lukaszewski, H. A New Stable Free Radical. Tetrahedron Lett. 1968, 9, 2701–2705. are gaining much interest due to their properties, such as exceptional stability, spin Π-delocalization, narrow electrochemical window and low excitation energies. For these reasons, a rapidly increasing attention is given to these radicals as structural elements of advanced materials.Jasiński, M.; Szczytko, J.; Pociecha, D.; Monobe, H.; Kaszyński, P. "Substituent-dependent magnetic behavior of discotic benzo[e][1,2,4]triazinyls", J. Am. Chem. Soc. 2016, 138, 9421-9424. Kapuściński, S.; Gardias, A.; Pociecha, D.; Jasiński, M.; Szczytko, J.; Kaszyński, P. "Paramagnetic bent-core mesogens derived from the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl", J. Mater. Chem. C, 2018, 6, 3079–3088.heir design requires, however, a good understanding of the electronic structure of these electro-, photo- and magnetically active molecular components. Recent advances in the chemistry of the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl demonstrated access to the parent “planarized” Blatter radical, in which more effective spin delocalization onto the Ph ring at the N(1) position is observed.Kaszyński, P.; Constantinides, C. P.; Young, V. G. The Planar Blatter Radical: Structural Chemistry of 1,4-Dihydrobenzo[e][1,2,4]triazin-4-yls. Angew. Chem. 2016, 128, 11315–11318.n order to better understand the impact of electronic delocalization on properties of the radicals, a series of derivatives has been prepared and investigated by computational and spectroscopy methods. Herein we present determination of the electronic structure of a series of substituted planar radical using UV photoelectron spectroscopy (UV-PES), EPR, and UV-vis spectroscopy.

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Footnotes:

Blatter, H. M.; Lukaszewski, H. A New Stable Free Radical. Tetrahedron Lett. 1968, 9, 2701–2705.) Jasiński, M.; Szczytko, J.; Pociecha, D.; Monobe, H.; Kaszyński, P. "Substituent-dependent magnetic behavior of discotic benzo[e][1,2,4]triazinyls", J. Am. Chem. Soc. 2016, 138, 9421-9424. Kapuściński, S.; Gardias, A.; Pociecha, D.; Jasiński, M.; Szczytko, J.; Kaszyński, P. "Paramagnetic bent-core mesogens derived from the 1,4-dihydrobenzo[e][1,2,4]triazin-4-yl", J. Mater. Chem. C, 2018, 6, 3079–3088.T Kaszyński, P.; Constantinides, C. P.; Young, V. G. The Planar Blatter Radical: Structural Chemistry of 1,4-Dihydrobenzo[e][1,2,4]triazin-4-yls. Angew. Chem. 2016, 128, 11315–11318.I