The linear dicarbon phosphide molecule (CCP) has a ²Π ground electronic state with a small spin-orbit splitting into ²Π_1/2 and ²Π_3/2 states. It has a reasonably large dipole moment and has been observed in interstellar space. We have studied CCP⁻ ion using high-resolution photoelectron imaging and observed dipole-bound excited states for CCP⁻ right below the detachment threshold. Resonant photoelectron spectra have been obtained by exciting the anion to specific vibrational levels of the dipole-bound states. We have observed a dipole-bound state for each spin-orbit state and the vibrational autodetachment is state-selective, providing the first spectroscopic evidence that the dipole-bound electron does not couple to the neutral core.

Spectra of ethylene dimers and trimers are studied in the ν₁₁ and (for the dimer) ν₉ fundamental band regions of C₂H₄ ( ∼ 2990 and 3100 cm⁻¹) using a tunable optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. The deuterated trimer has been observed previously, but this represents the first rotationally resolved spectrum of (C₂H₄)₃. The results support the previously determined cross-shaped (D_2d) dimer and barrel-shaped (C_3h or C₃) trimer structures. However, the dimer spectrum in the ν₉ fundamental region of C₂H₄ is apparently very perturbed and a previous rotational analysis is not well verified.

Oxytocin (OT) is the first structure-identified peptide hormone, which has a cyclic part formed by disulfide-bridge and a C-terminal α-amidated tail. Since some studies show that oxytocin alleviates mental disorders and postpartum hemorrhage, it has been developed as pharmaceuticals, recently more focused on oral drugs. However, low membrane permeability of oxytocin impedes its oral administration. One of the important factors which affect the membrane permeability is how dehydrated structure in the membrane changes into the hydrated structure. In this work, to elucidate the effect of the hydration on oxytocin structure, infrared spectroscopy was employed on isolated hydrated oxytocin clusters (OTH⁺· (D₂O)_n, n=1-4), combining with theoretical calculations. The results of this study suggest that the hydration of only a single water molecule interrupts the intramolecular hydrogen bond between the cyclic moiety and the tail part. The structural deformation by the hydration will be discussed.

Borazine, also referred to as inorganic benzene, displays an interesting case study of non-covalent interactions involving the N-H group as well as the π-system, unlike the benzene system, whose interaction is dominated by only the π-system. Borazine is a multifunctional molecule with the N-H serving as a proton donor and the partially delocalized π electron cloud as a proton acceptor. The interaction of borazine with various π systems, such as acetylene, benzene and phenylacetylene was studied experimentally, using matrix isolation IR spectroscopy and computationally, using ab initio calculations. Computations were carried out at the M06-2X and MP2 levels of theory using both 6-311++G** and aug-cc-pVDZ basis sets. In the case of all the π systems studied in our work, the N-H group of borazine was found to serve as the proton donor. In the case of both borazine-acetylene and borazine-phenylacetylene, a bent NH...C structure, where the N-H of borazine was the proton donor to the carbon of the acetylenic group was found to be the global minimum. However, in the case of borazine-benzene, a parallel displaced structure was found to be the global minimum at both levels of theory. Borazine was also different from benzene in that it displayed some unconventional bonding scenarios such as the dihydrogen bond in the borazine dimer and a boron bond in the borazine-water systems. Details of the experimental data and computational results will be presented.

In an effort to determine the feasibility of producing hydrogen gas via H₂O + C₂H₄ → H₂ + CH₃CHO, cluster reactivity studies were completed between Mo_xO_y cluster anions and H₂O, C₂H₄, and mixtures of both H₂O and C₂H₄. These studies unveiled the evolution of several chemifragmentation products. To better understand the molecular-scale interactions along these chemifragmentation pathways, the photoelectron spectra and supporting theoretical calculations were analyzed for each cluster. In this talk, spectra and computational results for a series of monometallic chemifragment cluster anions formed from reactions with C₂H₄ will be presented. The analysis indicates that experimental spectra are most consistent with η²−acetylene complexes, however vinylidene complexes cannot be definitively ruled out for all clusters. The results of this work deepen our understanding of the side reactions which occur in this multi-reactant system.

This talk focuses on the mass resolved- resonant 2-photon ionization (R2PI), resonant ion-dip infrared spectroscopy (RIDIR) and IR-UV holeburning (IR-UV HB) spectroscopy of propylbenzene(pBz)-(H₂O)_n clusters and the comparison with their Benzene(Bz)-(H₂O)_n cluster counterparts, which are a well-studied prototype system for the π H-bond. Since the pBz monomer exists in gauche and trans conformers, one anticipates the presence of pBz-H₂O complexes with H₂O on the same or opposite sides of the ring as the gauche or trans propyl chain. Indeed, local minima associated with these four complexes were identified by dispersion-corrected DFT calculations. R2PI and IR-UV HB spectra of pBz-H₂O show long Franck-Condon progressions associated with the set of conformers of the complex. The OH stretch RIDIR spectra consist of a single transition in the symmetric stretch region, and a doublet with varying spacing in the antisymmetric stretch region, indicating coupling to a large-amplitude motion (LAM). The changes in the OH stretch region indicate that the water molecule bound to propylbenzene undergoes more restricted motion on the π cloud than its Bz-H₂O counterpart. The potential energy surface for H₂O tumbling on the pBz π cloud was mapped out, and used as the basis for calculating from first principles the OH stretch infrared spectrum. Comparison with the spectrum for Bz-H₂O further illustrates the source and restrictions of the LAM of H₂O in pBz compared to Bz. OH stretch IR spectra of the higher water clusters pBz-(H₂O)_n with n=3, 4 are very similar to their Bz-(H₂O)_n counterparts, existing as H-bonded cycles, with no evidence of LAM on the aromatic π cloud.

Weakly bound complexes containing aromatic species have been the subject of study for many years. Here, a study of the 1:1 complexes of furan () with water will be presented. In this work, matrix isolation FTIR and computational methods were used to examine stable geometries of this dimer system. Density functional theory and MP2 methods were used to identify four minimum energy geometries. Three interaction motifs are recognized in these structures: , , and . The four structures were found to be within 610 cm⁻¹(7.3 kJ/mol) of each other across all computational methods. Matrix isolation FTIR spectroscopy was used to explore mixtures of furan with in a nitrogen matrix at 15 K. Spectra acquired show several peaks that were not associated with water or furan monomers and have been assigned to FUW. Additionally, mixtures of furan with and HDO were deposited and their spectra recorded. Characteristic shifts of each isotopologue were identified and used to characterize the geometry of the FUW complex. Both computational and spectroscopic results point to the formation of a single complex geometry that interacts through a standard hydrogen bond.

Matrix isolation infrared spectroscopy was used to characterize a 1:1 complex of hydrogen peroxide (H₂O₂) with benzene (C₆H₆). Co-deposition experiments with H₂O₂ and C₆H₆ were performed at 20 K using argon as the matrix gas. New infrared peaks attributable to the H₂O₂-C₆H₆ complex were observed near the O-H stretching vibrations and the OH bending vibrations of the H₂O₂ monomer and near the hydrogen out-of-plane bending vibration of the C₆H₆ monomer. The initial identification of the newly observed infrared peaks to those of a H₂O₂-C₆H₆ complex was established by performing several concentration studies in which the sample-to-matrix ratios of the monomers were varied between 1:100 to 1:1600, by comparing the resulting co-deposition spectra with the spectra of the individual monomers, and by matrix annealing experiments (30 – 35 K). Co-deposition experiments were also performed using isotopically labeled hydrogen peroxide (D₂O₂ and HDO₂) and benzene (C₆D₆) and the analogous peaks for the isotopically labelled complexes were observed. Quantum chemical calculations were performed for the H₂O₂-C₆H₆ complex at the MP2/aug-cc-pVDZ level of theory in order to explore the intermolecular potential energy surface of the complex and to obtain optimized complex geometries and predicted vibrational frequencies of the complex, which were compared to the experimental infrared spectra.