Browsing by Subject "MOLECULAR-HYDROGEN"

Sort by: Order: Results:

Now showing items 1-5 of 5
  • Zhivonitko, Vladimir V.; Sorochkina, Kristina; Chernichenko, Konstantin; Kotai, Bianka; Foldes, Tamas; Papai, Imre; Telkki, Ville-Veikko; Repo, Timo; Koptyug, Igor (2016)
    The parahydrogen-induced polarization (PHIP) phenomenon, observed when parahydrogen is used in H-2 addition processes, provides a means for substantial NMR signal enhancements and mechanistic studies of chemical reactions. Commonly, noble metal complexes are used for parahydrogen activation, whereas metal-free activation is rare. Herein, we report a series of unimolecular metal-free frustrated Lewis pairs based on an ansa-aminoborane (AAB) moiety in the context of PHIP. These molecules, which have a "molecular tweezers'' structure, differ in their substituents at the boryl site (-H, -Ph, -o-iPr-Ph, and -Mes). PHIP effects were observed for all the AABs after exposing their solutions to parahydrogen in a wide temperature range, and experimental measurements of their kinetic and thermodynamic parameters were performed. A theoretical analysis of their nuclear spin polarization effects is presented, and the roles of chemical exchange, chemical equilibrium and spin dynamics are discussed in terms of the key dimensionless parameters. The analysis allowed us to formulate the prerequisites for achieving strong polarization effects with AAB molecules, which can be applied for further design of efficient metal-free tweezers-like molecules for PHIP. Mechanistic (chemical and physical) aspects of the observed effects are discussed in detail. In addition, we performed quantum chemical calculations, which confirmed that the J-coupling between the parahydrogen-originated protons in AAB-H-2 molecules is mediated through dihydrogen bonding.
  • Mattila, K.; Haas, M.; Haikala, L. K.; Jo, Y-S.; Lehtinen, K.; Leinert, Ch.; Väisänen, P. (2018)
    Context. Dark nebulae display a surface brightness because dust grains scatter light of the general interstellar radiation field (ISRF). High-galactic-latitudes dark nebulae are seen as bright nebulae when surrounded by transparent areas which have less scattered light from the general galactic dust layer. Aims. Photometry of the bright dark nebulae LDN 1780, LDN 1642, and LBN 406 shall be used to derive scattering properties of dust and to investigate the presence of UV fluorescence emission by molecular hydrogen and the extended red emission (ERE). Methods. We used multi-wavelength optical photometry and imaging at ground-based telescopes and archival imaging and spectroscopic UV data from the spaceborn GALEX and SPEAR/FIMS instruments. In the analysis we used Monte Carlo RT and both observational data and synthetic models for the ISRF in the solar neighbourhood. The line-of-sight extinctions through the clouds have been determined using near infrared excesses of background stars and the 200/250 mu m far infrared emission by dust as measured using the ISO and Herschel space observatories. Results. The optical surface brightness of the three target clouds can be explained in terms of scattered light. The dust albedo ranges from similar to 0.58 at 3500 angstrom to similar to 0.72 at 7500 angstrom. The spectral energy distribution of LDN 1780 is explained in terms of optical depth and background scattered light effects instead of the original published suggestion in terms of ERE. The far-ultraviolet surface brightness of LDN 1780 cannot be explained by scattered light only. In LDN 1780, H-2 fluorescent emission in the wavelength range 1400-1700 angstrom has been detected and analysed. Conclusions. Our albedo values are in good agreement with the predictions of the dust model of Weingartner and Draine and with the THEMIS CMM model for evolved core-mantle grains. The distribution of H-2 fluorescent emission in LDN 1780 shows a pronounced dichotomy with a strong preference for its southern side where enhanced illumination is impinging from the Sco OB2 association and the O star zeta Oph. A good correlation is found between the H-2 fluorescence and a previously mapped 21-cm excess emission. The H-2 fluorescence emission in LDN 1780 has been modelled using a PDR code; the resulting values for H-2 column density and the total gas density are consistent with the estimates derived from CO observations and optical extinction along the line of sight.
  • Abergel, A.; Juvela, M.; Kurki-Suonio, H.; Lähteenmäki, Anne; Suur-Uski, A. -S.; Valiviita, J.; Planck Collaboration (2014)
  • Chernichenko, K.; Kotai, B.; Nieger, M.; Heikkinen, S.; Papai, I.; Repo, T. (2017)
    2-(Dialkylamino) phenylboranes containing the BXZ group, where X, Z = C6F5, Cl, and H, were prepared in a few synthetic steps and demonstrated the cleavage of H-2 under mild conditions. Depending on the nature of the dialkylamino group, X, and Z, the stability of the produced zwitterionic H-2 adducts varies from isolated solids indefinitely stable in an inert atmosphere to those quickly equilibrating with the initial aminoborane and H-2. Using a combined experimental/computational approach on a series of isostructural aminoboranes (dialkylamino = 2,2,6,6-tetramethylpiperid-1-yl), it was demonstrated that the electro-negativity and the steric effect of the substituents generally follow the trend C6F5 similar to Cl >> H. This observation is useful for designing new FLPs for practical applications. As an example, we demonstrated the hydrogenation of alkynes to cis-alkenes under mild conditions that was catalyzed by a chloro-analogue of the C6F5-substituted aminoborane developed previously. The presence of a BHCl group in the amino-chloroboranes or in their H-2 adducts features facile redistribution of the H and Cl atoms and the formation of polychloro and polyhydrido species.
  • Väisänen, Petri; Reunanen, Juha; Kotilainen, Jari; Mattila, Seppo; Johansson, Peter H.; Ramphul, Rajin; Romero-Canizales, Cristina; Kuncarayakti, Hanindyo (2017)
    We present new SINFONI near-infrared (NIR) integral field unit (IFU) spectroscopy and Southern African Large Telescope (SALT) optical long-slit spectroscopy characterizing the history of a nearby merging luminous infrared galaxy, dubbed the Bird (IRAS19115-2124). TheNIR line-ratio maps of the IFU data cubes and stellar population fitting of the SALT spectra now allow dating of the star formation (SF) over the triple system uncovered from our previous adaptive optics data. The distinct components separate clearly in line-ratio diagnostic diagrams, both thermal and non-thermal excitation is present. An off-nuclear starburst dominates the current SF of the Bird with 60-70 per cent of the total, with a 4-7 Myr age. The most massive nucleus, in contrast, is quenched with a starburst age of >40 Myr and shows hints of budding active galactic nucleus (AGN) activity. The secondary massive nucleus is at an intermediate stage. The two major components have signs of an older stellar population, consistent with a starburst triggered 1 Gyr ago in a first encounter. The simplest explanation of the history is that of a triple merger, where the strongly star-forming component has joined later. We detect multiple gas flows. The Bird offers an opportunity to witness multiple stages of galaxy evolution in the same system; triggering as well as very recent quenching of SF, and, perhaps, an early appearance of AGN activity. It also serves as a cautionary note on interpretations of observations with lower spatial resolution and/or without infrared data. At high redshift the system would look like a clumpy starburst with crucial pieces of its puzzle hidden in danger of misinterpretations.