SAND IN THE LABORATORY. PRODUCTION AND INTERROGATION OF GAS PHASE SILICATES.

Given its technological importance, the literature abounds with models for plasma enhanced chemical vapor deposition of the SiH$_4$/O$_2$/Ar system. In a continuing effort to identify and characterize the optical spectra of Si$_3$ generated in a SiH$_4$/Ar pulsed discharge sourcefootnote{The electronic spectrum of Si$_3$ I: the triplet D$_{3h}$ system� Reilly, N. J.; Kokkin, D. L.; Zhuang, X.; Gupta, V.; Nagarajan, R.; Fortenberry, R. C.; Maier, J. P.; Steimle, T. C.; Stanton, J. F.; McCarthy, M. C., J. Chem. Phys. 136(19), 194307, 2012.}, we detected, via two dimensional (2D) LIF, a relatively strong electronic transition in the 570-600,nm region that is strongly enhanced by the addition of a small amount of O$_2$. The excitation spectrum shows resolved band structure at the pulsed laser resolution of 0.5,cm$^{-1}$ and exhibits a radiative lifetime of 1.97,$mu$s. The dispersed fluorescence exhibits three vibrational progressions and an unusually small splitting of approximately 50,cm$^{-1}$. Here we report on efforts to identify the molecular carrier of these bands, with particular interest paid to species resulting from oxygen impurities in the silane discharge

THE QUINTESSENTIAL BOND OF MODERN SCIENCE. THE DETECTION AND CHARACTERIZATION OF DIATOMIC GOLD SULFIDE, AuS.

The gold sulfur bond is becoming ever more important to a vast range of scientific endeavors. We have recorded the electronic spectrum of gas-phase AuS, at vibrational resolution, over the 440-740,nm wavelength range. By application of a synergy of production techniques, hot hollow-cathode sputtering source and cold laser ablation molecular beam source, excitation from both spin components of the inverted $^2Pi$ ground state is possible. Excitation into four different excited electronic states involving approximately 100 red-degraded bands has been observed. The four excited states have been characterized as $a^4Sigma_{1/2}$, $A^2Sigma^+_{1/2}$, $B^2Sigma^-_{1/2}$ and $C^2Delta_i$. The observed red-degraded vibronic bands where then globally analyzed to determine an accurate set of term energies and vibrational constants for the excited and ground electronic states. The electronic configurations from which these states arise will be discussed

The optical spectrum of a large isolated polycyclic aromatic hydrocarbon: hexa-peri-hexabenzocoronene, C42H18

The first optical spectrum of an isolated polycyclic aromatic hydrocarbon large enough to survive the photophysical conditions of the interstellar medium is reported. Vibronic bands of the first electronic transition of the all benzenoid polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene were observed in the 4080-4530 Angstrom range by resonant 2-color 2-photon ionization spectroscopy. The strongest feature at 4264 Angstrom is estimated to have an oscillator strength of f=1.4x10^-3, placing an upper limit on the interstellar abundance of this polycyclic aromatic hydrocarbon at 4x10^12 cm^-2, accounting for a maximum of ~0.02% of interstellar carbon. This study opens up the possibility to rigorously test neutral polycyclic aromatic hydrocarbons as carriers of the diffuse interstellar bands in the near future.Comment: 9 pages, 1 figure. Fixed a typo on the frequency of the 'b' ban

Application of two dimensional flourescence spectroscopy to transition metal clusters

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.9]{NiONiO2.eps} \end{wrapfigure} Determining the physical properties (bond lengths, angles, dipole moments, etc) of transition metal oxides and dioxides is relevant to catalysis, high temperature chemistry, materials science and astrophysics. Analysis of optical spectra is a convenient method for extraction of physical properties, but can be difficult because of the density of electronic states and in the case of the dioxides, presence of both the oxide and superoxide forms. Here we demonstrate the application of two dimensional fluorescence spectroscopy\footnote{N.J. Reilly, T.W. Schmidt, S.H. Kable, \textit{J. Phys. Chem. A.}, 110(45), 12355-12359, 2006} for aiding in the assignment and analysis. Particular attention will be paid to the spectroscopy of first row transition metal monoxides and dioxides of Nickel, NiO and NiO$_2$, and Manganese, MnO. Furthermore, the application of this technique to discovering the spectrum of other transition metal systems such as Metal-dicarbides will be outlined

THE OPTICAL SPECTRUM OF THIOZONE S3_3 AND OTHER SULFUR RICH SYSTEMS

J. R. Spencer, K. L. Jessup, M. A. McGrath, G. E. Ballester and R. Yelle, \textit{ScienceA. Mollet, E. Lellouch, R. Moreno, M. A. Gurwell and C. Moore, \textit{A\&AP. Geissler, A. McEwen, C. Porco, D. Strobel, J. Saur, J. Ajello and R. West, \textit{IcarusAuthor Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden St.; Cambridge, MA 02138, and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138The recent discovery and mapping of S$_2$ and SO$_2$ in the plume of Pele, one of the largest and most active volcanoes on Io, the innermost moon of Jupiter, suggests that other sulfur rich molecules may be abundant in this unusual planetary source., \underline{\textbf{288}}, 1208-1210, 2008}$^,$, \underline{\textbf{482}}, 279-292, 2008} Optical images of Io in the range 3900\,{\AA} - 5000\,{\AA} conclude as much: the observed flux intensity cannot be attributed to transitions of these molecules alone., \underline{\textbf{172}}, 127-140, 2004} By means of 2-colour resonant-2-photon ionisation time of flight mass spectroscopy the optical spectrum of thiozone S$_3$ and other sulfur rich systems have now been detected. For thiozone a progression in the excited state bending mode is seen with a frequency of 350\,cm$^{-1}$ built onto the origin band at 433.82\,nm. In this talk our results are compared to prior experimental matrix and low-resolution gas-phase work. The prospects for finding these atomic clusters in the atmosphere of Io will be discussed

Probing Cooperativity In C–H⋯N and C–H⋯π Interactions: Dissociation Energies Of Aniline⋯(CH\u3csub\u3e4\u3c/sub\u3e)\u3csub\u3en\u3c/sub\u3e (n = 1, 2) van der Waals Complexes From Resonant Ionization And Velocity Mapped Ion Imaging Measurements

Recent studies of the weakly bound anisole⋯CH4 complex found a dual mode of binding, featuring both C/H⋯π and C/H⋯O noncovalent interactions. In this work, we examine the dissociation energies of related aniline⋯(CH4)n (n = 1, 2) van der Waals clusters, where both C/H⋯π and C/H⋯N interactions are possible. Using a combination of theory and experiments that include mass-selected two-color resonant two-photon ionization spectroscopy, two-color appearance potential (2CAP) measurements, and velocity-mapped ion imaging (VMI), we derive the dissociation energies of both complexes in the ground (S0), excited (S1), and cation radical (D0) states. As the amide group is non-planar in the ground state, the optimized ground state geometry of the aniline⋯CH4 1:1 complex shows two isomers, each with the methane positioned above the aniline ring. The observed redshift of the electronic origin from the aniline monomer is consistent with TDDFT calculations for the more stable isomer, where the methane sits on the same face as the amino hydrogens. The dissociation energies of the 1:1 complex, obtained from 2CAP measurements, are in good agreement with the calculated theoretical values from selected density functional theory methods. VMI data for the 1:1 complex gave a binding energy value overestimated by ∼179 cm−1 when compared to the 2CAP results, indicating that dissociative ionization selectively populates an excited vibrational level of the aniline cation radical. Given that the electron donating ability of aromatic substituents trends as –NH2 \u3e –OCH3 \u3e –CH3, it is noteworthy that the strength of methane binding also trends in this order, as found by experiment (dissociation energies in kJ/mol: 6.6 \u3e 5.8 \u3e 4.5) and predicted by theory (PBE0-D3/def2-QZVPPD, in kJ/mol: 6.9 \u3e 6.0 \u3e 5.0). For the 1:2 complex of aniline and methane, calculations predict that the more stable conformer is the one where the two methane molecules lie on opposite faces of the ring, consistent with the observed redshift of the electronic origin. Unlike the anisole–methane 1:2 complex, which shows an enhanced dissociation energy for the loss of one methane in comparison with the 1:1 complex, here, we find that the energy required to remove one methane from the ground state aniline–methane 1:2 complex is smaller than that of the 1:1 complex, consistent with theoretical expectations

OPTICAL SPECTROSCOPY OF SILICON-CARBON CLUSTERS: Si2_2C and Si3_3C

Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden St.; Cambridge, MA 02138, and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford; St., Cambridge, MA 02138We report the first measurement of an electronic spectrum of Si$_2$C, observed in a jet-cooled discharge through silane, acetylene and argon, in the $380-410$\,nm wavelength range. While Si$_2$C is a highly plausible astronomical molecule, searches for its rotational transitions in the laboratory and in space are impractical at present - \emph{ab initio} predictions of the rotational constants of this slightly bent species have yet to performed to within the required accuracy. By analogy with SiC$_2$, the carrier of the well-known Merrill-Sanford bands, electronic spectroscopy may provide estimates of its rotational constants and structure, thereby constraining searches for its millimeter-wave transitions. Our experiments suggest that the electronic transition has a large oscillator strength and a significant fluorescence quantum yield, making it a good candidate for optical detection in space, particularly in those carbon stars where SiC$_2$ is known to be abundant. As part of a more general effort to measure the electronic spectra of small silicon-carbon clusters, several examples of which have been identified in space by radio-astronomy, we present a spectrum of Si$_3$C with a much higher S/N ratio than has been previously reported, and which is now in excellent agreement with theory

Unraveling a Trifecta of Weak non-Covalent Interactions: The Dissociation Energy of the Anisole-Ammonia 1:1 Complex

The anisole-ammonia 1:1 complex is a challenge for both experiment and theory. Early studies supported a non-planar structure, involving a trifecta of weak non-covalent interactions: N-H/O, N-H/π, and C-H/N. The calculated structure and binding energy of the complex proved remarkably sensitive to the level of theory employed. Here, we report the first experimental measurement of the ground state dissociation energy of the complex, and derive an excited (S1) state dissociation energy that is in excellent agreement with the cutoff observed in the experimental excitation spectrum. Results are compared with previous predictions and new calculations based on benchmarked Density Functional Theory methods

IDENTIFYING FLUORESCENT HYDROCARBON RADICALS FROM A BENZENE DISCHARGE

Author Institution: School of Chemistry, University of Sydney, NSW 2006, AustraliaWe have applied the tools of laser induced fluorescence and dispersed fluorescence to the products of a benzene discharge in a free jet with a view to identifying new hydrocarbon radicals. We have observed several new band systems in the visible and UV regions, including a putative origin at 4759\AA (air) which fluoresces to a ground state exhibiting vibrational modes at 120\,cm$^{-1}$, 821\,cm$^{-1}$, 988\,cm$^{-1}$ and 1160\,cm$^{-1}$. This species is of particular interest due to its proximity to the centre of the (very) diffuse interstellar band at 4761.7\AA\ (FWHM 25\AA)