Equilibrium Values for the Si-H Bond Length and Equilibrium Structures of Silyl Iodide and Halosilylenes.

The equilibrium structures of silyl iodide, SiHI, and silylene halides, SiHX (X = F, Cl, Br, I), were determined by using the mixed regression method, where approximate values of the rotational constants are supplemented by the structural parameters of a different origin. For this goal, it is shown that the r(Si-H) bond length can be determined by using the isolated SiH stretching frequency and that an accurate estimation of the bond angles is obtained by an MP2 calculation with a basis set of triple zeta quality. To check the accuracy of the experimental structures, they were also optimized by means of all electron CCSD(T) calculations using basis sets of quadruple zeta quality.

Single-photon ionization of SiC in the gas phase: experimental and characterization of SiC.

We report the first experimental observation of single-photon ionization transitions of the SiC radical between 8.0 and 11.0 eV performed on the DESIRS beamline at the SOLEIL synchrotron facility.

Dynamics of the isotope exchange reaction of D with H , HD, and DH.

We have measured the merged-beams rate coefficient for the titular isotope exchange reactions as a function of the relative collision energy in the range of ∼3 meV-10 eV. The results appear to scale with the number of available sites for deuteration. We have performed extensive theoretical calculations to characterize the zero-point energy corrected reaction path.

Reactivity of Hydrated Hydroxide Anion Clusters with H and Rb: An ab Initio Study.

We present a theoretical investigation of the hydrated hydroxide anion clusters, OH(HO), and of the collisional complexes, H-OH(HO) and Rb-OH(HO) (with = 1-4). The MP2 and CCSD(T) methods are used to calculate interaction energies, optimized geometries, and vertical detachment energies. Parts of the potential energy surfaces are explored with a focus on the autodetachment region.

Vibronic structure of the cyanobutadiyne cation. I. VUV photoionization study of HCN.

We report the vacuum-ultraviolet threshold-photoelectron spectrum of HCN recorded over a wide spectral range, from 84 000 to 120 000 cm, with a 120 cm spectral resolution, better than what was achieved in previous photoelectron studies, and with mass selectivity. The adiabatic ionization potential of cyanobutadiyne is measured at 85 366 (±40) cm. Assignment of the vibrational bands of the four lowest electronic states XΠ, AΠ, BΣ, and CΠ are performed, supported by high level ab initio calculations which are fully detailed in Paper II [B.

Vibronic structure of the cyanobutadiyne cation. II. Theoretical exploration of the complex energy landscape of HCN.

The results of an extensive ab initio study of the cyanobutadiyne cation, initially motivated by threshold-photoelectron spectroscopy experiments [see the study by Gans et al., J. Chem.

Heliaphen, an Outdoor High-Throughput Phenotyping Platform for Genetic Studies and Crop Modeling.

Heliaphen is an outdoor platform designed for high-throughput phenotyping. It allows the automated management of drought scenarios and monitoring of plants throughout their lifecycles. A robot moving between plants growing in 15-L pots monitors the plant water status and phenotypes the leaf or whole-plant morphology.

Experimental and theoretical investigations of HO-Ar.

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of HO-Ar in the 2OH excitation range of HO. 24 sub-bands have been observed. Their rotational structure (T = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ=0.

Ab initio study of the neutral and anionic alkali and alkaline earth hydroxides: Electronic structure and prospects for sympathetic cooling of OH.

We have performed a systematic ab initio study on alkali and alkaline earth hydroxide neutral (MOH) and anionic (MOH) species where M = Li, Na, K, Rb, Cs or Be, Mg, Ca, Sr, Ba. The CCSD(T) method with extended basis sets and Dirac-Fock relativistic effective core potentials for the heavier atoms has been used to study their equilibrium geometries, interaction energies, electron affinities, electric dipole moment, and potential energy surfaces. All neutral and anionic species exhibit a linear shape with the exception of BeOH, BeOH, and MgOH, for which the equilibrium structure is found to be bent.

Experimental and ab initio characterization of HCN vibronic structure. I. Synchrotron-based threshold photo-electron spectroscopy.

Threshold-photoionization spectroscopy of cyanoacetylene (HCN) and its N isotopologue has been investigated in the vacuum-ultraviolet range with a synchrotron-based experiment allowing to record threshold-photoelectron spectrum and photoion yield over a large energy range (from 88 500 to 177 500 cm, i.e., from 11 to 22 eV).

Experimental and ab initio characterization of HCN vibronic structure. II. High-resolution VUV PFI-ZEKE spectroscopy.

Vacuum-ultraviolet pulsed-field-ionization zero-kinetic-energy photoelectron spectra of XΠ2←XΣ+1 and BΠ2←XΣ+1 transitions of the HCN and HCN isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed us to resolve the vibrational structures and the spin-orbit splittings in the cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (E/hc(HCN)=93 909(2) cm and E/hc(HCN)=93 912(2) cm), the vibrational frequencies of the ν, ν, and ν vibrational modes, and the spin-orbit coupling constant (A = -44(2) cm) of the XΠ2 cationic ground state have been derived from the measurements.

Ab initio study of reactive collisions between Rb((2)S) or Rb((2)P) and OH(-)((1)Σ(+)).

A theoretical rate constant for the associative detachment reaction Rb((2)S) + OH(-)((1)Σ(+)) → RbOH((1)Σ(+)) + e(-) of 4 × 10(-10) cm(3) s(-1) at 300 K has been calculated. This result agrees with the experimental rate constant of 2-1 (+2)×10(-10)cm(3)s(-1) obtained by Deiglmayr et al. [Phys.

Potential energy surface and bound states of the NH3-Ar and ND3-Ar complexes.

A new, four-dimensional potential energy surface for the interaction of NH3 and ND3 with Ar is computed using the coupled-cluster method with single, double, and perturbative triple excitations and large basis sets. The umbrella motion of the ammonia molecule is explicitly taken into account. The bound states of both NH3-Ar and ND3-Ar are calculated on this potential for total angular momentum values from J = 0 to 10, with the inclusion of Coriolis interactions.

Sequence dependence of electron-induced DNA strand breakage revealed by DNA nanoarrays.

The electronic structure of DNA is determined by its nucleotide sequence, which is for instance exploited in molecular electronics. Here we demonstrate that also the DNA strand breakage induced by low-energy electrons (18 eV) depends on the nucleotide sequence. To determine the absolute cross sections for electron induced single strand breaks in specific 13 mer oligonucleotides we used atomic force microscopy analysis of DNA origami based DNA nanoarrays.

Theoretical description of electronically excited vinylidene up to 10 eV: first high level ab initio study of singlet valence and Rydberg states.

The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0-10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems.

Electron-attachment-induced DNA damage: instantaneous strand breaks.

Low energy electron-attachment-induced damage in DNA, where dissociation channels may involve multiple bonds including complex bond rearrangements and significant nuclear motions, is analyzed here. Quantum mechanics/molecular mechanics (QM/MM) calculations reveal how rearrangements of electron density after vertical electron attachment modulate the position and dynamics of the atomic nuclei in DNA. The nuclear motions involve the elongation of the P-O (P-O(3') and P-O(5')) and C-C (C(3')-C(4') and C(4')-C(5')) bonds for which the acquired kinetic energy becomes high enough so that the neighboring C(3')-O(3') or C(5')-O(5') phosphodiester bond may break almost immediately.

Ab initio calculation of the rotational spectrum of methane vibrational ground state.

In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame.

Determination of the ground electronic state in transition metal halides: ZrF.

The spectroscopy of the ZrF radical, produced by a laser ablation-molecular beam experimental setup, has been investigated for the first time using a two-color two-photon (1 + 1') REMPI scheme and time-of-flight (TOF) mass spectrometry detection. The region of intense bands 400-470 nm has been studied, based upon the first spectroscopic observations of the isovalent ZrCl radical by Carroll and Daly. The overall spectrum observed is complex.

The search for a deterministic origin for the presence of nonracemic amino-acids in meteorites: a computational approach.

Amino-acid enantiomeric excesses (ee's) have been detected in different types of carbonaceous chondrites, all in favor of the L enantiomer. In this article, we discuss possible deterministic causes to the presence of these amino-acid ee's in meteorites and evaluate in particular enantioselective photolysis by circularly polarized light (CPL). The electronic circular dichroism spectra of a set of amino- and hydroxy-acids, all detected in chondritic matter but some with ee's and others without ee's, were calculated and compared.

Conformations consistent with charge migration observed in DNA and RNA X-ray structures.

Electron holes are known to migrate along the DNA or RNA duplexes and to localize preferentially on successive guanines. The stationary point conformations of Gua pairs that can trap or let pass these holes have been characterized by quantum chemistry calculations. Here we show their recurrent occurrence in DNA and RNA X-ray structures, often in quadruplex conformations or in interaction with proteins, ligands or metal ions.

Comparison of the experimental, semi-experimental and ab initio equilibrium structures of acetylene: influence of relativisitic effects and of the diagonal Born-Oppenheimer corrections.

The equilibrium structure of acetylene (also named ethyne) has been reinvestigated to resolve the small discrepancies noted between different determinations. The size of the system as well as the large amount of available experimental data provides the quite unique opportunity to check the magnitude and relevance of various contributions to equilibrium structure as well as to verify the accuracy of experimental results. With respect to pure theoretical investigation, quantum-chemical calculations at the coupled-cluster level have been employed together with extrapolation to the basis set limit, consideration of higher excitations in the cluster operator, inclusion of core correlation effects as well as relativistic and diagonal Born-Oppenheimer corrections.

Radiative lifetime of the a 3Σ+ state of HeH+ from ab initio calculations.

The first metastable triplet state of HeH(+) was found to be present in ion beam experiments, with its lifetime estimated to be between hundreds of milliseconds and thousand of seconds. In this work, we use ab initio methods to evaluate the radiative lifetimes of the six vibrational levels of the a (3)Σ(+) of HeH(+). The transition a (3)Σ(+)→X (1)Σ(+) is spin-forbidden, but acquires intensity through spin-orbit interaction with the singlet and triplet Π states.

Ab initio study of the electron transfer in an ionized stacked complex of guanines.

The charge transfer process in an ionized stacking of two consecutive guanines (G(5')G(3'))(+) has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G(5')G(3'))(+) is governed by the avoiding crossing between the ground and first excited states of the complex.