Unpredictable Dynamic Behaviour of Ruthenium Chelate Pyrrole Derivatives.

Reaction of [Ru(H)(CO)(PPh)] with an equimolar amount of pyrrole-2-carboxylic acid () leads to the homoleptic chelate derivative k(O,O)-[RuH(CO)(HL)(PPh)] . Prolonged acetonitrile refluxing promotes an unusual k(O,O)- → k(N,O)- dynamic chelate conversion, forming a neutral, stable, air- and moisture- insensitive, solvento-species k(N,O)-[Ru(MeCN)(CO)(L)(PPh)] . Analogously, reaction of with the pyrrole-2-carboxyaldehyde () affords k(N,O)-[RuH(CO)(HL)(PPh)] , , as a couple of functional isomers.

Spectroscopic detection of the gallium methylene (GaCH2 and GaCD2) free radical in the gas phase by laser-induced fluorescence and emission spectroscopy.

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2-2B1 electronic transition.

Ru-Controlled Thymine Tautomerization Frozen by a k(O)-, k(N,O)-Metallacycle: An Experimental and Theoretical Approach.

The reaction of -(Ru(H)(CO)(PPh)) () with one equivalent of thymine acetic acid (THAcH) unexpectedly produces the macrocyclic dimer k(O), k(N,O)-(Ru(CO)(PPh)THAc) () and, concomitantly, the doubly coordinated species k(O), k(O,O)-(Ru(CO)(PPh)THAc) (). The reaction promptly forms a complicated mixture of Ru-coordinated mononuclear species. With the aim of shedding some light in this context, two plausible reaction paths were proposed by attributing the isolated or spectroscopically intercepted intermediates on the basis of DFT-calculated energetic considerations.

Which triatomic monohalosilylenes, monohalogermylenes, and monohalostannylenes (HMX) fluoresce or phosphoresce and why? An ab initio investigation.

The possibilities of emission from the ÃA″ and ãA″ excited states of the triatomic halosilylenes, halogermylenes, and halostannylenes (HMX, M = Si, Ge, Sn; X = F, Cl, Br, I) have been explored in a series of extensive ab initio calculations. The triplet states are found to have deep bonding wells supporting an extensive manifold of vibrational levels, which could give rise to observable triplet-singlet phosphorescence. The ã-X̃ band systems of the halosilylenes are calculated to occur at the red edge of the visible and are likely to be very weak.

Ab initio spectroscopy of the aluminum methylene (AlCH) free radical.

Extensive ab initio investigations of the ground and electronic excited states of the AlCH free radical have been carried out in order to predict the spectroscopic properties of this, as yet, undetected species. Difficulties with erratic predictions of the ground state vibrational frequencies, both in the literature and in the present work, have been traced to serious broken-symmetry instabilities in the unrestricted Hartree-Fock orbitals at the ground state equilibrium geometry. The use of restricted open-shell Hartree-Fock or complete active space self consistent field orbitals avoids these problems and leads to consistent and realistic sets of vibrational frequencies for the ground state.

A stimulated emission study of the ground state bending levels of BH through the barrier to linearity and ab initio calculations of near-spectroscopic accuracy.

The ground state bending levels of BH have been studied experimentally using a combination of low-resolution emission spectroscopy and high-resolution stimulated emission pumping (SEP) measurements. The data encompass the energy range below, through, and above the calculated position of the barrier to linearity. For the bending levels (0,3,0) and above, the data show substantial K-reordering, with the K = 1 levels falling well below those with K = 0.

Effect of Noncovalent Interactions on Vibronic Transitions: An Experimental and Theoretical Study of the C H⋅⋅⋅CO Complex.

We report on the experimental and theoretical infrared spectrum of the C H⋅⋅⋅CO complex. This complex was prepared by UV photolysis of propiolic acid (HC OOH) in argon and krypton matrices. The experimental bands of C H in the C H⋅⋅⋅CO complex are blue-shifted from those of the C H monomer.

An experimental and theoretical study of the Ã(2)A(″)Π-X̃(2)A(') band system of the jet-cooled HBBr/DBBr free radical.

The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr3 vapor and H2 or D2 in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra.

BH2 revisited: New, extensive measurements of laser-induced fluorescence transitions and ab initio calculations of near-spectroscopic accuracy.

The spectroscopy of gas phase BH2 has not been explored experimentally since the pioneering study of Herzberg and Johns in 1967. In the present work, laser-induced fluorescence (LIF) spectra of the Ã(2)B1(Πu)-X̃ (2)A1 band system of (11)BH2, (10)BH2, (11)BD2, and (10)BD2 have been observed for the first time. The free radicals were "synthesized" by an electric discharge through a precursor mixture of 0.

An experimental and theoretical study of the electronic spectrum of the HBCl free radical.

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F.

An experimental and theoretical study of the electronic spectrum of HPS, a second row HNO analog.

The à (1)A" - X (1)A' electronic spectra of jet-cooled HPS and DPS have been observed for the first time, using a pulsed discharge jet source. Laser induced fluorescence spectra were obtained in the 850-650 nm region. Although the 0(0)(0) band was not observed, strong 3(0)(n) and 2(0)(1)3(0)(n) progressions and 3(1) hot bands could be assigned in the HPS LIF spectrum.

Ab initio quartic force field of stannane and rotational analysis of the ν1 infrared band of H(120)SnD3.

Stannane, SnH(4), has been studied both theoretically, using high-level ab initio methods, and experimentally, using high-resolution spectroscopy to analyze the Sn-H stretching fundamental band of the H(120)SnD(3) isotopologue. The geometry and the anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations level of theory. H(120)SnD(3), present as minor isotopologue in (120)SnD(4), has been studied by Fourier transform spectroscopy at an effective resolution of ca.

Heavy atom nitroxyl radicals. VI. The electronic spectrum of jet-cooled H2PO, the prototypical phosphoryl free radical.

The previously unknown electronic spectrum of the H(2)PO free radical has been identified in the 407-337 nm region using a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio predictions of the properties of the ground and first two excited doublet states were used to identify the spectral region in which to search for the electronic transition and were used to aid in the analysis of the data. The band system is assigned as the B̃(2)A(')-X̃(2)A(') electronic transition which involves promotion of an electron from the π to the π∗ molecular orbital.

Heavy atom nitroxyl radicals. V. An experimental and ab initio study of the previously unknown H2PS free radical.

The B̃(2)A(')-X̃(2)A(') transition of the prototypical thiophosphoryl radical, H(2)PS, was observed for the first time using laser-induced fluorescence and single vibronic level emission spectroscopy. H(2)PS and its deuterated isotopologues, D(2)PS and HDPS, were produced in a pulsed supersonic discharge jet from a precursor mixture of Cl(3)PS and H(2) or D(2) or an H(2)/D(2) mixture in high-pressure argon. High level ab initio calculations of the lowest three doublet electronic states helped in the definitive assignment of the B̃-X̃ transition, which involves electron promotion from the π to the π∗ orbital.

Vibronic coupling in the A2Π and B2Σ+ electronic states of the NCS radical.

The spin-rovibronic energy levels of the A(2)Π and B(2)Σ(+) electronic states of thiocyanate radical have been calculated variationally, using high-level ab initio coupled diabatic potential energy surfaces. Computations up to J = 7∕2 have been performed, obtaining all levels with K ≤ 3 (Σ(1/2),Π(1/2,3/2),Δ(3/2,5/2),Φ(5/2,7/2)), for energies up to 2000 cm(-1) above the A(000)(2)Π(3∕2) level. The available experimental data have been critically reviewed in the light of the theoretical findings.

Giant Renner-Teller vibronic coupling in the BF2 radical: an ab initio study of the X (2)A1 and A (2)Pi electronic states.

The potential energy surfaces (PESs) of the ground X (2)A(1) and the first excited A (2)Pi (1 (2)B(1), 2 (2)A(1)) electronic states of the BF(2) radical have been studied ab initio, using a large basis set and CCSD(T) and EOM-CCSD techniques. The calculated PESs were used to variationally calculate the energy levels up to approximately 36,000 cm(-1) above the ground state. The Renner-Teller splitting parameter (epsilon=0.

Heavy atom nitroxyl radicals. IV. Experimental and theoretical studies of the F(2)P=S free radical in the gas phase.

The difluorothiophosphoryl (F(2)PS) free radical has been produced in a supersonic discharge jet from a precursor mixture of F(3)PS and high pressure argon and detected by laser-induced fluorescence and single vibronic level emission spectroscopy. With the aid of high level ab initio predictions of the properties of the ground and first two excited doublet states, the observed band system has been positively identified as B(2)A(')-X(2)A('). The electronic transition involves promotion of an electron from the pi to the pi( *) orbital with concomitant increases in the out-of-plane angle and PS bond length on excitation.

Calculations of rovibrational energies and dipole transition intensities for polyatomic molecules using MULTIMODE.

We report rigorous calculations of rovibrational energies and dipole transition intensities for three molecules using a new version of the code MULTIMODE. The key features of this code which permit, for the first time, such calculations for moderately sized but otherwise general polyatomic molecules are briefly described. Calculations for the triatomic molecule BF(2) are done to validate the code.

Heavy atom nitroxyl radicals. III. Identification of the Cl(2)P=S free radical in the gas phase by laser spectroscopy and ab initio calculations.

The dichlorothiophosphoryl (Cl(2)PS) free radical has been identified in the gas phase for the first time by a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio calculations of the properties of the ground and first two excited states have been undertaken to aid in the interpretation of the data. The radicals were produced by an electric discharge through a dilute mixture of Cl(3)PS in high pressure argon at the exit of a pulsed supersonic expansion.

Heavy atom nitroxyl radicals. I: An ab initio study of the ground and lower electronic excited states of the H(2)As=O free radical.

A series of ab initio calculations have been undertaken to predict the spectroscopic properties of the ground and first two excited states of the recently discovered arsenyl (H(2)AsO) free radical. This 13 valence electron species can be viewed as similar to the formaldehyde radical anion with a ground state electron configuration of cdots, three dots, centered(pi)(2)(n)(2)(pi( *))(1). The arsenyl radical is nonplanar (pyramidal) in the ground state with a 59 degrees out-of-plane angle and a 1.

The electronic spectrum of the fluoroborane free radical. I. Theoretical calculation of the vibronic energy levels of the ground and first excited electronic states.

The fluoroborane (HBF) free radical has a large vibronic interaction which splits the orbitally degenerate (2)Pi state in the linear configuration into two separate electronic states, one strongly bent and one linear. The observed vibrational structure of the electronic transition between the Renner-Teller pair of states is very complex. As an aid to understanding the spectrum, the vibronic energy levels of the ground and first excited states have been calculated from high-level ab initio potential energy surfaces using a variational method.

Ab initio anharmonic force field and rotational analyses of infrared bands of perchloryl fluoride.

Perchloryl fluoride, FClO(3), has been studied both experimentally and theoretically, using high-resolution Fourier transform spectroscopy and high-level ab initio methods. The geometry, dipole moment, and anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory. The infrared spectra of monoisotopic species have been recorded.

Order parameters of alpha,omega-diphenylpolyenes in a nematic liquid crystal from an integrated computational and 13C NMR spectroscopic approach.

The orientational order parameters and conformational behavior of five relatively large rodlike molecules, biphenyl, trans-stilbene, 1,3-diphenyl-butadiene, 1,3,5-diphenyl-hexatriene, and 1,3,5,7-diphenyl-octatetraene, dissolved in the thermotropic liquid crystal ZLI-1167, have been studied using an integrated approach combining (13)C NMR measurements and quantum mechanical computations of carbon chemical shift tensors. Besides biphenyl, the phenyl moiety of all structures has been found to have a high rotational mobility in the temperature range of the present experiments. The rank-two order parameter in the nematic phase is found to increase steadily from the shortest to the longest term of the series at any temperature within the nematic range.

A combined theoretical and experimental approach to determining order parameters of solutes in liquid crystals from 13C NMR data.

The ordering properties of an anisotropic liquid crystal can be studied by recording 13C NMR spectra at different temperatures for a number of rigid solutes. The traditional difficulty in analyzing 13C data comes from the scarcity of experimental information about the carbon shielding tensors and from their limited transferability among different solutes. We show that these obstacles can be overcome by computing high-level ab initio shielding tensors, also including the solvent effects by the polarizable continuum model.

Ab initio prediction of the infrared-absorption spectrum of the C2Cl radical.

The three lowest (1(2)A', 2(2)A', and 1(2)A") potential-energy surfaces of the C2Cl radical, correlating at linear geometries with 2Sigma+ and 2Pi states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the 12C12C35Cl isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm(-1), using diabatic potential-energy and dipole moment surfaces and a recently developed variational method.