Although cumulene carbenes terminated with sulfur up to H₂C₇S are known to possess C_2v geometries, the analogous oxygen species have only been characterized in the gas-phase up to H₂C₄O, and propadienone (H₂C₃O) and butatrienone (H₂C₄O) exhibit kinked heavy atom backbones. Using microwave spectral taxonomy, searches have been undertaken for pentatetrenone (H₂C₅O) and its isomers. Surprisingly, no evidence has been found for the cumulenone, but rotational lines of a bent-chain isomer, HC(O)C₄H, analogous in structure to propynal, HC(O)CCH, have been detected instead. In closely-related work, the sulfur analog HC(S)C₄H has also been identified for the first time. This talk will provide a summary of our search procedure and experimental findings, quantum chemical calculations of isomeric stability and dipole moments, and prospects for detecting these longer chains in astronomical sources where c-C₃H₂O and HC(O)CCH are known.

An important step in combustion processes is the abstraction of hydrogen to form alkyl benzyl radicals. In this talk we present the results of double resonance spectroscopy methods to explore the conformation-specific infrared spectroscopy of α-methylbenzyl, α-ethylbenzyl, and α-propylbenzyl radicals. A local mode-Hamiltonian model that includes Fermi resonance interactions will be described. This model enables the assignment of the alkyl CH stretch IR spectra of these molecules. This talk will contrast the alkyl chain results to their closed shell analogues, focusing on the the role of the radical site which leads to two important effects. First the CH-stretch frequencies of the β-carbons are shifted by approximately 50 cm⁻¹. Second, internal torsion about the C-C bond between the α-C and β-C atoms modulates these frequency shifts, this producing torsion-vibration mixing. The spectral consequences of this mixing are described.

In this study, we calculate the spectrum of the OH stretch overtone region in CH₃OOH using vibrational second-order perturbation theory. Comparison of the calculated to the experimental spectra shows very good agreement. With this in place, the goal of this study is to use second-order perturbation theory to investigate the following questions. To begin with, we explored the origins of the transition strength and found that both mechanical and electrical anharmonicities contribute to the overall intensity. Then we studied the amount of OO stretch and OH stretch character in the wavefunctions that correspond to the states that are accessed by the experiment. This is of interest because the VMP (vibrationally mediated photodissociation) action spectrum of CH₃OOH is obtained by detection of the OH radical following vibrational excitation of the overtones/combination bands and the subsequent photodissociation along the OO bond. Interestingly, OH is detected in its vibrationless state following excitation of the OH and CH stretch overtones and combination bands involving the OH stretch. In contrast, vibrationally excited OH is only detected following excitation of OH stretch overtones in methyl peroxide. To further understand the origins of the intensity in CH₃OOH, we also explored the effects of deuteration in the OH and CH overtone regions.

Model compounds continue to play crucial roles for elucidating the ubiquitous phenomena of hydrogen bonding and proton transfer, often yielding invaluable insights into kindred processes taking place in substantially larger species. The symmetric double-minimum topography that characterizes the potential-energy landscape for an important subset of these systems allows unambiguous signatures of molecular dynamics (in the form of tunneling-induced bifurcations) to be extracted directly from spectral measurements. As a relatively unexplored member of this class, 6-hydroxy-2-formylfulvene (HFF) contains an intramolecular O–H···O interaction that has participating atoms from the hydroxylic (donor) and ketonic (acceptor) moieties closely spaced in a quasi-linear configuration. This unusual arrangement suggests proton transduction to occur with minimal encumbrance, possibly leading to a pronounced dislocation of the shuttling hydron commensurate with the concepts of low-barrier hydrogen bonding (which are distinguished by great strength, short distance, and vanishingly small potential barriers). A variety of spectroscopic probes built primarily upon the techniques of laser-induced fluorescence and dispersed fluorescence have been enlisted to acquire the first vibronically resolved information reported for the ground [~X¹A₁] and lowest-lying singlet excited [ùB₂ (π*π)] electronic manifolds of HFF entrained in a cold supersonic free-jet expansion. These experimental findings will be discussed and compared to those obtained for related proton-transfer systems, with complimentary quantum-chemical calculations serving to unravel the unique bonding motifs and reactive pathways inherent to HFF.

It has been found in our previous works that rotational and fine-structure analysis of spectra involving nearly degenerate electronic states may aid in interpretation and analysis of the vibronic structure, specifically in the case of pseudo-Jahn-Teller (pJT) molecules with C_s symmetry. The spectral analysis of pJT derivatives (isopropoxyJ. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013)nd cyclohexoxyJ. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871-11890 (2014) of a prototypical JT molecule (the methoxy radical) allowed for quantitative determination of various contributions to the energy separation between the nearly degenerate electronic states, including the relativistic spin-orbit (SO) effect, the electrostatic interaction, and their zero-point energy difference. These states are coupled by SO and Coriolis interactions, which can also be determined accurately in rotational and fine structure analysis. Most recently, the spectroscopic model for rotational analysis of pJT molecules has been extended for analysis of molecules with C₁ symmetry, i.e., no symmetry. This model includes the six independently determinable components of the spin-rotation (SR) tensor and the three components of the SO and Coriolis interactions. It has been employed to simulate and fit high-resolution laser-induced fluorescence (LIF) spectra of jet-cooled alkoxy radicals with C₁ symmetry, including the 2-hexoxy and the 2-pentoxy radicals, as well as previously recorded LIF spectrum of the trans-conformer (defined by its OCCC dihedral angle) of the 2-butoxy radical.L. Stakhursky, L. Zu, J. Liu, and T. A. Miller, J. Chem. Phys. 125, 094316 (2006)lthough the LIF spectra can be reproduced by using either the SR constants or SO and Coriolis constants, the latter simulation offers results that are physically more meaningful whereas the SR constants have to be regarded as effective constants. Furthermore, we will review the SO and Coriolis constants of alkoxy radicals that have been investigated, starting from the well-studied methoxy radical (CH₃O).

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J. Liu, D. Melnik, and T. A. Miller, J. Chem. Phys. 139, 094308 (2013)a J. Liu and T. A. Miller, J. Phys. Chem. A 118, 11871-11890 (2014)) L. Stakhursky, L. Zu, J. Liu, and T. A. Miller, J. Chem. Phys. 125, 094316 (2006)A

Metal-containing free radicals are important intermediates in metal-surface reactions and in the interaction between metals and organic molecules. In the present work, dispersed fluorescence (DF) spectra of the calcium ethoxide radical (CaOC₂H₅) have been obtained by pumping the òA′← X̃²A′ and the B̃²A" ← X̃²A′ origin bands in its laser-induced fluorescence (LIF) spectrum. CaOC₂H₅ radicals were produced by 1064 nm laser ablation of calcium grains in the presence of ethanol under jet-cooled conditions. Dominant transitions in the vibrationally resolved DF spectra are well reproduced using Franck-Condon factors predicted by complete active space self-consistent (CASSCF) calculations. Differences in transition intensities between the òA′→ X̃²A′ and the B̃²A" → X̃²A′ DF spectra are attributed to the pseudo-Jahn-Teller interaction between the à ² A′ and the B̃ ² A" states. Collision-induced population transfer between these two excited electronic states results in additional peaks in the DF spectra.

r0pt Figure Electron photodetachment of O⁻(²P_3/2,1/2) is measured using velocity-map imaging at wavelengths near 350 nm, where detachment yields both O(¹D₂) and O(³P_2,1,0) atoms, simultaneously, producing slow ( ∼ 0.1 eV) and fast electrons ( ∼ 2 eV). The photoelectron spectrum resolves the fine-structure transitions, which together with the well known atomic fine-structure splittings,physics.nist.gov/cgi-bin/ASD/energy1.plnd intensity ratios,O. Scharf and M. R. Godefried, arXiv:0808.3529v1rovide an excellent test of the spectral quality of the velocity-map imaging technique. Although the photoelectron angular distribution for the two atomic limits have the same negative anisotropy sign, the energy dependence differs. The variation is qualitatively in accordance with R-matrix cross section calculations, that indicate a more gradual d-wave onset for the ¹D limit.O. Zatsarinny and K. Bartschat, Phys. Rev. A, 73, 022714 (2006). doi:10.1103/PhysRevA.73.022714owever, more exact evaluation is only possible with information about the matrix element phases.

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physics.nist.gov/cgi-bin/ASD/energy1.pla O. Scharf and M. R. Godefried, arXiv:0808.3529v1p O. Zatsarinny and K. Bartschat, Phys. Rev. A, 73, 022714 (2006). doi:10.1103/PhysRevA.73.022714H

The photodetachment spectrum of BeO⁻ has been studied using high resolution velocity map imaging photoelectron spectroscopy. The vibrational contours were imaged and compared with Franck-Condon simulations for the ground and excited states of the neutral. The electron affinity of BeO was measured for the first time, and anisotropies of several transitions were determined. Experimental findings are compared to high level ab initio calculations.

In this talk, the power and synergy of combining experimental measurements with density functional theory computations as a single tool to unambiguously characterize the molecular structure of complex atomic systems is shown. Here, we bring three beautiful cases where the interaction between the experiment and theory is in very good agreement for both finite and extended systems: 1) Characterizing Metal Coordination Environments in Porous Organic Polymers: A Joint Density Functional Theory and Experimental Infrared Spectroscopy StudyJ.M. López-Encarnación, K.K. Tanabe, M.J.A. Johnson, J. Jellinek, Chemistry–A European Journal 19 (41), 13646-13651 2) Characterization of Rhenium Compounds Obtained by Electrochemical Synthesis After Aging ProcessA. Vargas-Uscategui, E. Mosquera, J.M. López-Encarnación, B. Chornik, R. S. Katiyar, L. Cifuentes, Journal of Solid State Chemistry 220, 17-21 and 3) Infrared Study of H(D)₂ + Co₄⁺ Chemical Reaction: Characterizing Molecular Structures.

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J.M. López-Encarnación, K.K. Tanabe, M.J.A. Johnson, J. Jellinek, Chemistry–A European Journal 19 (41), 13646-13651; A. Vargas-Uscategui, E. Mosquera, J.M. López-Encarnación, B. Chornik, R. S. Katiyar, L. Cifuentes, Journal of Solid State Chemistry 220, 17-21;

We report preliminary ab initio electronic structure calculations of HBr and HBr⁺. The computations were carried out employing the MRD-CI package, with a basis set of cc-pVQZ quality augmented with s-, p- and d-type diffuse functions. In a first series of calculations, without inclusion of spin-orbit splitting, potential energy curves of about 20 doublet and quartet electronic states of HBr⁺, and about 30 singlet and triplet (valence and Rydberg) states of HBr were computed. This exploratory step provides a perspective of the character, shape, leading configurations, energetics, and asymptotic behaviour of the electronic states. The calculations taking into account spin-orbit are currently being performed. Our study focuses mainly on the Rydberg states and their interactions with the repulsive valence states and with the bound valence ion-pair state. In particular, the current calculations seek to provide information that might be relevant to the interpretation of recent REMPI measurementsD. Zaouris, A. Kartakoullis, P. Glodic, P. C. Samartzis, H. R. Hródmarsson, Á. Kvaran, Phys. Chem. Chem. Phys., 17, 10468 (2015).hich involve the interaction between the diabatic E¹Σ⁺ Rydberg state and the diabatic V¹Σ⁺ ion-pair state (which together constitute the adiabatic, double-well, B¹Σ⁺ state). Several new states of both HBr and HBr⁺ are reported.

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D. Zaouris, A. Kartakoullis, P. Glodic, P. C. Samartzis, H. R. Hródmarsson, Á. Kvaran, Phys. Chem. Chem. Phys., 17, 10468 (2015).w

Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) has been used to characterize adsorbed species widely but reaction intermediates rarely on electrodes. In previous studies, the observed SERS signals were proposed from surface benzyl species due to the electrochemical reduction of benzyl chloride on silver electrode surfaces. In this work, we reinvestigated the vibrational assignments of benzyl chloride and benzyl radical as the reaction intermediate. On the basis of density functional theoretical (DFT) calculations and normal mode analysis, our systematical results provide more reasonable new assignments for both surface species. Further, we investigated adsorption configurations, binding energies, and vibrational frequency shifts of benzyl radical interacting with silver. Our calculated results show that the wagging vibration displays significant vibrational frequency shift, strong coupling with some intramolecular modes in the phenyl ring, and significant changes in intensity of Raman signals. The study also provides absolute Raman intensity in benzyl halides and discuss the enhancement effect mainly due to the binding interaction with respect to free benzyl radical.

The observed surface-enhanced Raman scattering (SERS) spectra of water adsorbed on metal film electrodes of silver, gold, and platinum nanoparticles were used to infer interfacial water structures. The basis is the change of the electrochemical vibrational Stark tuning rates and the relative Raman intensity of the stretching and bending modes. How it is not completely understood the reason why the relative Raman intensity ratio of the bending and stretching vibrations of interfacial water increases at the very negative potential region. Density functional theory calculations provide the conceptual model. The specific enhancement effect for the bending mode was closely associated with the water adsorption structure in a hydrogen bonded configuration through its H-end binding to surface sites with large polarizability due to strong cathodic polarization. The present theoretical results allow us to propose that interfacial water molecules exist on these metal cathodes with different hydrogen bonding interactions, the HO-H…Ag(Au) for silver and gold. In acidic solution, a surface electron–hydronium ion-pair was proposed as an adsorption configuration of interfacial water structures on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H₃O⁺(H₂O)_ne⁻, where the hydronium H₃O⁺ and the surface electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Thus, Raman intensities of the interfacial water in the EHIP species are signifcantly enhanced due to the cathodic polarization on silver and gold electrodes.