The most simple solvated proton, the hydronium ion H₃O⁺ has been studied experimentally in its bare case as well as with the messenger techniques. Recent studies have shown that features in the vibrational spectra can be modulated not only by the different messengers, but also by the number of messengers. Theoretical molecular dynamics simulations have shed some light on the H₃O⁺(H₂)_n clusters, but understanding on the effect of microsolvaton by the messengers toward the spectra is still far from complete. We compare the experimental H₃O⁺Ar_m m=1-3 spectra with accurate theoretical simulations and oobtain the peak position and absorption intensity by solving the quantum vibrational Schrodinger equation using the potential and dipole moment obtained from DFT methods. One of the main goals of the study is to glean into the vibrational couplings induced by the microsolvation by the argon on the spectra region of 1500-3800 cm⁻¹, and to provide assignment on the peaks observed in these regions.

H₃O⁺ and H₅O₂⁺, Eigen and Zundel forms of the excess proton, are the basic moieties of hydrated proton in aqueous media. Using vibrational pre-dissotion spectra, vibrational spectra of messenager-tagged species are often measured; however, only neat species have been studied in detail by theoretical and computational means. To bridge this gap, we carry out extensive CCSD(T)/aug-cc-pvTZ calculations to investigate the binding between commonly used noble gas (NG) messenagers (He, Ne and Ar) with H₃O⁺ and H₅O₂⁺ to get an accurate estimate on the binding energy which yields the upper limits of vibrational temperature of NG-tagged clusters. The binding sites of NG and low-lying transition states have also been searched to give a better description on the energy landscape. In addition, a few exchange/correlation functionals have been tested to access the accuracy of these methods for future and more sophisticated theoretical studies.

There are two types of bands in the OH stretch region of the vibrational spectra of hydrogen-bonded complexes; narrow peaks due to isolated OH stretches and a broadened feature reflecting the OH stretches involved in strong hydrogen bonding. This second region can be as wide as several hundred wavenumbers and is shifted to the red of the narrow peaks. In this work we focus on H⁺(H₂O)_n, where n = 3 or 4.Relph, R. A.; Guasco, T. L.; Elliot, B. M.; Kamrath, M. Z.; McCoy, A. B.; Steele, R. P.; Schofield, D. P.; Jordan, K. D.; Viggiano, A. A.; Ferguson, E. E.; Johnson, M. A. Science, 2010, 327(5963), 308-312.oth of these systems exhibit a very intense, broad H-bonded band. This breadth arises from coupling between the OH stretches and the low frequency modes. To understand the broadening observed in the spectra, we have developed a computational scheme in which we sample displacement geometries from the equilibrium structure based on the ground state harmonic wavefunction.Johnson, C. J.; Dzugan, L. C.; Wolk, A. B.; Leavitt, C. M.; Fournier, J. A.; McCoy, A. B.; Johnson, M. A. J. Phys. Chem. A, 2014, 118, 7590-7597.hen we combine the harmonic spectra in the OH stretch region for each computed geometry to generate the spectrum for each protonated water structure. Based on the large anharmonicities at play in these modes, we extend the approach using second-order perturbation theory to solve the reduced-dimensional Hamiltonian that involves only the HOH bends and the OH stretches. This is done by expressing the normal modes used to expand the Hamiltonian as linear combinations of internal coordinates. In this talk we will describe the approach used for these anharmonic calculations and report preliminary results for these protonated water clusters.

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Footnotes:

Relph, R. A.; Guasco, T. L.; Elliot, B. M.; Kamrath, M. Z.; McCoy, A. B.; Steele, R. P.; Schofield, D. P.; Jordan, K. D.; Viggiano, A. A.; Ferguson, E. E.; Johnson, M. A. Science, 2010, 327(5963), 308-312.B Johnson, C. J.; Dzugan, L. C.; Wolk, A. B.; Leavitt, C. M.; Fournier, J. A.; McCoy, A. B.; Johnson, M. A. J. Phys. Chem. A, 2014, 118, 7590-7597.T

The effects of halogen and solvent on the conformer, vibrational and electronic properties of thiophene-2-carbaldehyde (C5H4OS) and thiophene-2-carbonyl-halogens [C5H3XOS; X = F, Cl or Br] were investigated employing the DFT and TD-DFT methods. The B3LYP functional was used with the 6-31++G(d,p) basis set. Computations were focused on the two conformational isomers of the compounds in the gas phase and both in a non-polar solvent and in a polar solvent. The present work explores the effects of both the halogen and the medium on the conformational preference, geometrical parameter, dipole moment, vibrational spectra, UV spectrum and HOMO-LUMO orbital. The findings of this work can be useful to those systems involving changes in the conformations analogous to the compounds studied.

Experimental and theoretical investigations have been performed on the structure, vibrational and electronic spectra of 5-quinolinecarboxaldehyde (5QC). The 4000-50 cm⁻¹region FT-IR and FT-Raman and the 190-1100 nm region UV–Vis spectra of 5QC were recorded at the room temperature. Structural and spectroscopic properties of the cis and trans conformers of 5QC were calculated by Hartree-Fock (HF) and B3LYP density functional methods using the 6-311++G(d,p) basis set. Although calculated B3LYP frequencies are found to be closer to the experimental frequencies than the HF calculation results, scaled frequencies of both HF and B3LYP levels are in good agreement with the experimental spectra. The time-dependent density functional theory (TDDFT) is also used to find excitation energies, absorption wavelength, oscillator strengths and HOMO and LUMO energies of the title molecule.
Keywords: FT-IR, FT-Raman, and UV-vis spectra; HF; DFT, HOMO-LUMO.
1. V. Kucuk, A. Altun, M. Kumru, Spectrochim. Acta Part A 85(2012)9298.
2. M. Kumru, V. Kucuk, T. Bardakci, Spectrochim. Acta Part A 90(2012)2834.
3. M. Kumru, V. Kucuk, M. Kocademir, Spectrochim. Acta Part A, 96 (2012) 242251.
4. M. Kumru, V. Kucuk, P. Akyürek, Spectrochim. Acta Part A, 113 (2013) 72–79.
5. M. Kumru, et al., Spectrochimica Acta Part A, 134 (2015) 81–89.
This work was supported by the Scientific Research Fund of Fatih University under the project number P50011001G (1457).

The dual florescence of dimethylaminobenzonitrile (DMABN) has been investigated since the 1960s. Despite more than 50 years of previous research, the spatial configuration of the excited state causing the dual fluorescence is still controversial. We have performed excited state calculations of DMABN in a variety of solvents of varying hydrogen-bonding affinity and polarity using implicit solvation (COSMO-PCM) at the M06-HF level of theory, and we have also collected steady-state absorption and fluorescence spectra of DMABN in these solvents. Our experimental spectra are broadly consistent with previous work, and the computational results show a significant solvent dependence.

Halocarbenes are organic reactive intermediates with a neutral divalent carbon atom that is covalently bonded with a halogen and another substituent. Being the smallest carbenes that exhibit closed shell ground states, they have contributed greatly to our understanding of the reactivity of singlet carbene species and the factors that contribute to singlet-triplet energy gaps. We report an analysis of spin-orbit coupling in the mono-halocarbenes, CH(D)X, where X = Cl, Br, I. Single Vibronic Level (SVL) emission spectroscopy and Stimulated Emission Pumping (SEP) spectroscopy have been used to probe the ground vibrational level structures in these carbenes which have indicated the presence of perturbations involving the low-lying triplet state. In this talk, we present two approaches to model these interactions. Anharmonic constants, singlet-triplet gaps and geometry-dependent spin-orbit (SO) coupling surfaces were computed using high-level explicitly correlated methods such as CCSD(T)-F12b and MRCI-F12. These were used to evaluate SO coupling matrix elements and hence predict/fit mixed-perturbed singlet-triplet experimental levels. Results are also compared to those from a simpler model using a geometry-independent SO-constant.

Nature uses protonation to alter the structures and reactivities of molecules to facilitate various biological functions and chemical transformations. For example, in nucleobase repair and salvage processes, protonation facilitates nucleobase removal by lowering the activation barrier for glycosidic bond cleavage. Systematic studies of the structures of protonated 2'-deoxyribonucleotides and ribonucleotides may provide insight into the roles protonation plays in altering the nucleobase orientation relative to the glycosidic bond and sugar puckering. In this study, infrared multiple photon dissociation (IRMPD) action spectroscopy experiments in conjunction with electronic structure calculations are performed to probe the effects of protonation on the structures and stabilities of 2′-deoxyadenosine-5′-monophosphate (pdAdo) and adenosine-5′-monophosphate (pAdo). Photodissociation as a function of IR wavelength is measured to generate the IRMPD action spectra. Geometry optimizations and frequency analyses performed at the B3LYP/6-311+G(d,p) level of theory are used to characterize the stable low-energy structures and to generate their linear IR spectra. Single point energy calculations performed at the B3LYP/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels of theory provide relative stabilities of the optimized conformations. The structures accessed in the experiments are determined by comparing the calculated linear IR spectra for the stable low-energy conformers computed to the measured IRMPD action spectra. The effects of the 2′-hydroxyl moiety are elucidated by comparing the structures and IRMPD spectra of [pAdo+H]⁺ to those of its DNA analogue. Comparisons are also made to the deprotonated forms of these nucleotides and the protonated forms of the analogous nucleosides to elucidate the effects of protonation and the phosphate group on the structures.