Direct frequency comb measurement of OD + CO → DOCO kinetics

The kinetics of the hydroxyl radical (OH) + carbon monoxide (CO) reaction, which is fundamental to both atmospheric and combustion chemistry, are complex because of the formation of the hydrocarboxyl radical (HOCO) intermediate. Despite extensive studies of this reaction, HOCO has not been observed under thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observed deuteroxyl radical (OD) + CO reaction kinetics and detected stabilized trans-DOCO, the deuterated analog of trans-HOCO. By simultaneously measuring the time-dependent concentrations of the trans-DOCO and OD species, we observed unambiguous low-pressure termolecular dependence of the reaction rate coefficients for N_2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield

Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds

We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CWLeo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emis- sion arises from a region of 6 arcseconds in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a SiC bond in the dust formation zone and certainly both play a key role in the formation of SiC dust grains.Comment: To be published in the Astrophysical Journal Letters; Accepted May 6 201

Direct frequency comb measurement of OD + CO → DOCO kinetics

The kinetics of the hydroxyl radical (OH) + carbon monoxide (CO) reaction, which is fundamental to both atmospheric and combustion chemistry, are complex because of the formation of the hydrocarboxyl radical (HOCO) intermediate. Despite extensive studies of this reaction, HOCO has not been observed under thermal reaction conditions. Exploiting the sensitive, broadband, and high-resolution capabilities of time-resolved cavity-enhanced direct frequency comb spectroscopy, we observed deuteroxyl radical (OD) + CO reaction kinetics and detected stabilized trans-DOCO, the deuterated analog of trans-HOCO. By simultaneously measuring the time-dependent concentrations of the trans-DOCO and OD species, we observed unambiguous low-pressure termolecular dependence of the reaction rate coefficients for N_2 and CO bath gases. These results confirm the HOCO formation mechanism and quantify its yield

Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of Si-C bonds

We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30 m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CW Leo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emission arises from a region of 6'' in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a Si−C bond in the dust formation zone and certainly both play a key role in the formation of SiC dust grains.We thank spanish MINECO for funding under grants AYA2009-07304, AYA2012-32032, CSD2009-00038, and ERC under ERC-2013-SyG, G. A. 610256 NANOCOSMOS. The new laboratory measurements in Cambridge were supported by NASA grant NNX13AE59G

Convergent Functional Genomics of Schizophrenia: From Comprehensive Understanding to Genetic Risk Prediction

poster abstractWe have used a translational convergent functional genomics (CFG) approach to identify and prioritize genes involved in schizophrenia, by gene-level integration of genome-wide association study (GWAS) data with other genetic and gene expression studies in humans and animal models. Using this polyevidence scoring and pathway analyses, we identify top genes (DISC1, TCF4, MBP, MOBP, NCAM1, NRCAM, NDUFV2, RAB18, as well as ADCYAP1, BDNF, CNR1, COMT, DRD2, DTNBP1, GAD1, GRIA1, GRN2B, HTR2A, NRG1, RELN, SNAP-25, TNIK), brain development, myelination, cell adhesion, glutamate receptor signaling, G-protein coupled receptor signaling and cAMP- mediated signaling as key to pathophysiology and as targets for therapeutic intervention. Overall, the data is consistent with a model of disrupted connectivity in schizophrenia, resulting from the effects of neurodevelopmental environmental stress on a background of genetic vulnerability. In addition, we show how the top candidate genes identified by CFG can be used to generate a genetic risk prediction score (GRPS) to aid schizophrenia diagnostics, with predictive ability in independent cohorts. The GRPS also differentiates classic age of onset schizophrenia from early onset and late-onset disease. We also show, in three independent cohorts, two European-American (EA) and one African-American (AA), increasing overlap, reproducibility and consistency of findings from SNPs to genes, then genes prioritized by CFG, and ultimately at the level of biological pathways and mechanisms. Lastly, we compared our top candidate genes for schizophrenia from this analysis with top candidate genes for bipolar disorder and anxiety disorders from previous CFG analyses conducted by us, as well as findings from the fields of autism and Alzheimer. Overall, our work maps the genomic and biological landscape for schizophrenia, providing leads towards a better understanding of illness, diagnostics, and therapeutics. It also reveals the significant genetic overlap with other major psychiatric disorder domains, suggesting the need for improved nosology

LEAST SQUARES FITTING OF PERTURBED VIBRATIONAL POLYADS NEAR THE ISOMERIZATION BARRIER IN THE S1_1 STATE OF C2_2H2_2

Author Institution: Department of Chemistry, University of British Columbia, Vancouver, B.C., Canada V6T 1Z1; AND Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USAThe S$_1$ electronic state of acetylene has recently been shown to have two potential minima, corresponding to cis- and trans-bent structures. The trans-bent isomer is the more stable, with the cis-bent isomer lying about 2670 cm$^{-1}$ higher; the barrier to isomerization lies roughly 5000 cm$^{-1}$ above the trans zero-point level. The "isomerization coordinate'' (along which the molecule moves to get from the trans minimum to the barrier) is a combination of the $\nu_3$ (trans bending) and $\nu_6$ (cis bending) vibrational normal coordinates, but the spectrum is very confused because the $\nu_6$ vibration interacts strongly with the $\nu_4$ (torsion) vibration through Coriolis and Darling-Dennison resonances. Since the $\nu_4$ and $\nu_6$ fundamental frequencies are almost equal, nderline{\textbf{98}}, 2742, 1993.} the bending vibrational structure consists of polyads. At low vibrational energies the polyads where these three vibrations are excited can be fitted by least squares almost to experimental accuracy with a simple model of Coriolis and Darling-Dennison interactions, but at higher energies the huge $x_{36}$ cross-anharmonicity, which is a symptom that the levels are approaching the isomerization barrier, progressively destroys the polyad structure; in addition the levels show an increasing even-odd staggering of their $K$-rotational structures, as predicted by group theory. It is not possible to fit the levels near the barrier with a simple model, though some success has been achieved with extended models. Progress with the fitting of the polyads near the barrier will be reviewed

PATTERNS OF BROKEN PATTERNS

Author Institution: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Institute for Theoretical Chemistry, Departments of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712; Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan. Department of Chemistry, University of British Columbia, Vancouver, B.C., Canada V6T 1Z1Spectroscopy $-$ it is all about patterns. Some patterns look so indescribably complicated that, unlike pornography, you {\it do not} know one when you see one. It is tempting to say that, at high vibrational excitation, interactions among normal mode basis states are so strong and widespread that all patterns are obliterated. But this is not true. When normal mode frequencies are in near integer multiple ratios, polyads emerge. A polyad is a robust pattern often comprising many vibrational eigenstates. Each such pattern might span many hundreds of cm$^{-1}$, and it is inevitable that several unrelated polyad patterns overlap. When polyads overlap, it might seem impossible to disentangle them. However, the key to disentanglement is that polyads come in families in which successive generations are related by harmonic oscillator matrix element selection and {\it scaling rules}. Families of polyads are described by families of scaling-based effective Hamiltonian matrices, $\mathbf{H}^{\mathrm{eff}}$. No matter how complex and overlapped, the polyad $\mathbf{H}^{\mathrm{eff}}$ serves as a magic decoder for picking out the polyad pattern. Sometimes the polyad patterns are systematically broken (a meta-pattern), owing to proximity to an isomerization barrier, as occurs in highly excited bending levels of the S$_{1}$ state of HCCH, which encode the trans-cis minimum energy isomerization path. Quantum Chemists often dismiss $\mathbf{H}^{\mathrm{eff}}$ models, precisely because they are models that do not express the full dimensionality of the complete Hamiltonian. But an $\mathbf{H}^{\mathrm{eff}}$ explains rather than describes. Shunning $\mathbf{H}^{\mathrm{eff}}$s is like throwing out the baby with the bath water. Don't do it

REDUCED DIMENSION ROVIBRATIONAL VARIATIONAL CALCULATIONS OF THE S1_1 STATE OF C2_2H2_2

Author Institution: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Institute for Theoretical Chemistry, Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712; Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan; ; Department of Chemistry, University of British Columbia, B.C. V6T 1Z1, CanadaThe bending and torsional degrees of freedom in S$_1$ acetylene, C$_2$H$_2$, are subject to severe vibrational resonances and rovibrational interactions, which result in the low-energy vibrational polyad structure of these modes. As the internal energy approaches that of the barrier to \textit{cis-trans} isomerization, these energy level patterns undergo further large-scale reorganization that cannot be satisfactorily treated by traditional models tied to local equilibrium geometries. Experimental spectra in the region near the \textit{cis-trans} transition state exhibit these complicated new patterns. In order to rationalize our near-barrier observations and predict the detailed effects of \textit{cis-trans} isomerization on the rovibrational energy structure, we have performed reduced dimension rovibrational variational calculations of the S$_1$ state. Our calculation uses a high accuracy \textit{ab initio} potential surface and a fully symmetrized extended-CNPI group theoretical treatment of a multivalued internal coordinate system that is appropriate for bending and torsional large amplitude motions. We will discuss these results and the insights they offer on understanding both large-scale features and spectroscopic details, such as tunneling staggerings, of barrier-proximal rovibrational levels of the S$_1$ state. We will also discuss spectral features by which barriers can be located and characterized in general polyatomic systems