Near threshold photoionization of the ground and first excited states of C(2)

Calculations using the multichannel Schwinger configuration-interaction method are presented for the photoionization from the ground and the first excited states of the C(2) molecule. Both single channel and multichannel calculations are presented in a photon energy range from the threshold to about 50 eV of photon energy. For the ground state, inclusion of both intrinsic and dynamical correlation effects is seen to strongly alter the picture of the photoionization process inferred from single-channel frozen-core Hartree-Fock calculations. Furthermore, the photoionization study of the first excited state of molecular carbon has revealed the presence of strong interchannel coupling between the 3sigma(g)-->ksigma(u) channel and the photoionization channels leading to the A (4)Pi(g) and f (2)Pi(g) ionic states in the near threshold region.     

Near threshold channel selective photodissociation of NO2

The dynamics of the photodissociation of NO₂ into NO(X ²Π_Ω″, ν″=0,J″)+O(³ P _0,1,2) is investigated near the thermodynamic threshold. Cooling the internal degrees of freedom by a supersonic beam expansion provides a nearly complete quantum state selection prior to the predissociation. Measurements of the wavelength dependent dissociation yield into specific product quantum states are reported. At certain wavelengths Λ″ doublet resolved rotational population distributions of the fragments are obtained. Up to an excess energy ofE _exc=121 cm^?1 about 42% of this energy is partitioned into the rotation of the NO molecules, and correspondingly 58% into the translational degree of freedom. The role of electronic and total parity is discussed.     

Convolutamydine A: the first authenticated absolute configuration and enantioselective synthesis

The absolute configuration of (+)-convolutamydine A 1 isolated from Amathia convoluta has been unambiguously established as (R) by enantioselective synthesis, based on chiral auxiliary-directed π-face discrimination in an allyl metal addition to (1R,2S,5R)-8-phenylmenthyl ester 7. For an independent and unequivocal proof, the absolute stereochemistry of synthetic precursor 11 en route to 1 was determined by X-ray crystallography.     

The first synthesis and absolute configuration of glaucescenolide

The first synthesis of glaucescenolide (1), a cytotoxic sesquiterpene isolated from the liverwort, Schistochila glaucescens, was achieved by starting from 2,2,6-trimethylcyclohexanone (2). The absolute configuration of the naturally occurring 1 was confirmed as 5S,7S,10R.     

The first total synthesis of xenitorins B and C: assignment of absolute configuration

Starting from (-)-beta-pinene, the first total synthesis of xenitorins B and C has been accomplished, which also allowed the assignment of their absolute configuration.     

The first enantiospecific synthesis of (−)-heritol: absolute configuration determination

The first enantiospecific synthesis of (−)-heritol, from naturally occurring (R)-(+)-citronellal and confirmation of its absolute configuration, is described.     

The first total synthesis of putaminoxin and determination of its absolute configuration

Asymmetric synthesis of putaminoxin, a phytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of putaminoxin was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural putaminoxin.     

Near ab-initio methods for the calculations of large molecules: Comparison of pseudopotential and ab-initio results

Results from pseudopotential calculations on 5-hydroxyindole, tryptamine, 5-hydroxytryptamine, 6-hydroxytryptamine and the imidazolium cation are compared to full ab-initio calculations. The localization of all molecular orbitals is found to be identical with the two methods. Orbital energies from the two methods are found to be linearly correlated for all molecules: the slope is close to unity and the orbital energies from the pseudopotential calculation show a very slight and virtually constant shift to lower values. Electron density maps and molecular electrostatic potential maps calculated from the wavefunctions show that the charge distributions and molecular reactivity characteristics predicted by the two methods are nearly identical.     

Enantiospecific first total synthesis and confirmation of the relative and absolute stereostructure of isocalamusenone

The enantiospecific total synthesis of two epimers of the sesquiterpene isocalamusenone has been accomplished starting from the readily available monoterpene (R)-limonene, which of the natural product established the stereostructure and the absolute configuration.     

Phosphinites derived from the 7-phosphanorbornene skeleton: first results in asymmetric catalysis

[structure: see text] The bisphosphinite 4 incorporating two 7-phosphanorbornene subunits is an efficient ligand for the Rh-catalyzed enantioselective hydrogenation of functional alkenes in terms of rate and enantioselectivity. This type of structures is readily accessible by [4 + 2] cycloaddition of phospholes with dienophilic alkenes and can be easily fine-tuned.     

Digital pulse-shape discrimination applied to an ultra-low-background gas-proportional counting system: first results

A new ultra-low-background proportional counter design was recently developed at Pacific Northwest National Laboratory (PNNL). This design, along with an ultra-low-background counting system which provides passive and active shielding with radon exclusion, has been developed to complement a new shallow underground laboratory (~30 m water-equivalent) constructed at PNNL. After these steps to mitigate dominant backgrounds (cosmic rays, external gamma-rays, radioactivity in materials), remaining background events do not exclusively arise from ionization of the proportional counter gas. Digital pulse-shape discrimination (PSD) is thus employed to further improve measurement sensitivity. In this work, a template shape is generated for each individual sample measurement of interest, a “self-calibrating” template. Differences in event topology can also cause differences in pulse shape. In this work, the temporal region analyzed for each event is refined to maximize background discrimination while avoiding unwanted sensitivity to event topology. This digital PSD method is applied to sample and background data, and initial measurement results from a biofuel methane sample are presented in the context of low-background measurements currently being developed.     

Time-resolved study of excited states of N2 near its first ionization threshold

Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing (1)Σ(g)(-) state has been excited via the intermediate c(4) (v = 0) (1)Π(u) Rydberg state. We present the analysis of the band located at T(v) = 10,800.7 ± 2 cm(-1) with respect to the intermediate state, 126,366 ± 11 cm(-1) with respect to the ground state, approximately 700 cm(-1) above the first ionization threshold. From the analysis a rotational constant of B(v) = 1.700 ± 0.005 cm(-1) has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c(4) (0) and c(5) (0) states are 5.6 and 4.4 ns, respectively, while the b(') (12), c(')(4) (4, 5, 6), and c(')(5) (0) states all have lifetimes in the range of hundreds of picoseconds.     

The first asymmetric total syntheses and determination of absolute configurations of xestodecalactones B and C

The first efficient asymmetric total syntheses of xestodecalactones B and C have been accomplished in 10 steps with an overall yield of 22 and 20.2%, respectively. The key steps involve the utility of Evans oxazolidinone-mediated syn-aldol condensations to establish the C-9 configuration and the macrolide ring formation by intramolecular acylation. The absolute configurations of xestodecalactones B and C have been determined via these syntheses.     

Mass-analyzed threshold ionization spectroscopy of pyridine. Structural distortion in the first excited state

For the first time, vibrational spectra of the pyridine cation in the electronic ground state have been measured via several intermediate states (0(0), 16b0(2), 16b0(4), 6a0(1), 6b(1), 16a0(1), 10a0(1) and 12(1)) by Mass-Analyzed Threshold Ionization (MATI) spectroscopy. From the MATI spectra, the adiabatic ionization energy of pyridine has been determined to be 74,185 +/- 6 cm(-1) (9.1978 +/- 0.0008 eV). Several vibronic modes in the ionic ground state could be assigned for the first time. An intensity gain of vibrations having b1 symmetry could be observed by activating the ion ground state. Also, a breakdown of the "delta nu = 0 propensity rule" for the excitation via the 16b(2) and 16b(4) states of the first excited states are displayed in the recorded spectra. In conjunction with ab initio calculations these observations can be explained by a strong geometrical distortion along the 16b vibration in the first excited state, leading to a "boat distortion".     

Mass-analyzed threshold ionization spectroscopy of pyrimidine: determining the geometry in the first excited and the ionic ground states

Vibrational spectra of the pyrimidine cation in the electronic ground state were measured via several intermediate states of the first excited state (0⁰,16a¹, 16a², 16a⁴, 16b¹, 10b¹, 6b², 6a¹, 1¹, 4¹, 4² and 12¹) by mass-analyzed threshold ionization spectroscopy. For the first time, several vibrational modes could be assigned in the first excited and the ionic ground states. Anharmonic coupling is shown to occur in the first excited state due to Fermi resonance between the 1¹ and the 16a⁴ vibrations. From the results of the measurements and calculations presented here, pyrimidine is predicted to be planar in the first excited and the ionic ground states, and it belongs to the C_2V point group.     

Instationary polymerization technique—basic principles and first results

Basic principles of a new polymerization technique and the subsequent analysis of the resultant molar mass distribution for the direct determination of the rate constant for chain propagation are introduced. First results are presented for the bulk polymerization of methyl methacrylate at room temperature. It is demonstrated, that the correlation between the active life time of a radical chain and the number of propagation steps, L_act=k_p[M]t_act is valid in the case of instationary polymerization conditions too.     

The first nonempirical circular dichroism determination of the absolute configuration of N-phthalimidosulfoximines based on exciton coupling mechanism and a correlation with the absolute configuration of chiral sulfoxides

A simple nonempirical method for the assignment of absolute configuration of N-phthalimidosulfoximines and related S-chiral sulfoxides, based on exciton-coupled circular dichroism, is presented.     

Density cumulant functional theory: first implementation and benchmark results for the DCFT-06 model

Density cumulant functional theory [W. Kutzelnigg, J. Chem. Phys. 125, 171101 (2006)] is implemented for the first time. Benchmark results are provided for atoms and diatomic molecules, demonstrating the performance of DCFT-06 for both nonbonded and bonded interactions. The results show that DCFT-06 appears to perform similarly to coupled cluster theory with single and double excitations (CCSD) in describing dispersion. For covalently bound systems, the physical properties predicted by DCFT-06 appear to be at least of CCSD quality around equilibrium geometries. The computational scaling of both DCFT-06 and CCSD is O(N(6)), but the former has reduced nonlinearities among the variables and a Hermitian energy functional, making it an attractive alternative.