Mátrixizolációs infravörös spektroszkópiai vizsgálatok = Matrix isolation infrared spectroscopic investigations

Kutatási eredményeinket két fő csoportra lehet osztani. Az eredmények egyik részét légkörkémiai vagy asztrokémiai szempontból érdekes gyökök valamint reaktív, egzotikus molekulák előállítása és spektroszkópia vizsgálata adja. Alkil-nitritek fotolízise során sikerült kimutatni az alkoxigyököt, mint köztiterméket, amerikai-magyar együttműködésben pedig alkil-peroxigyökök spektrumát analizáltuk. Ezek az eredmények segítséget nyújthatnak e specieszek légköri monitorálásához, illetve további kinetikai mérésekhez. Elsőként előállítottuk az asztrofizikusok és a preparatív kémikusok számára is érdekes tiofulminsavat (HCNS), illetve ennek származékait, pl. az FCNS-t. Ez az első olyan vizsgálat, amelyben egy nitril-szulfid N-S nyújtási rezgését sikerült kimérni. Eredményeink másik csoportjába modellpeptidek mátrixizolációs konformációanalízise sorolható. Mátrixizolációs infravörös (MI-IR) és az általunk elsők között alkalmazott mátrixizolációs rezgési circuláris dikroizmus (MI-VCD) spektroszkópiával alfa- és beta-peptidekmodellek, illetve ezek vízzel alkotott komplexeit vizsgáltuk. Többek között megmutattuk, hogy bár a beta-peptidek flexibilisebbek, mint a megfelelő alfa-peptidek, az erős hidrogénkötés miatt mégis csak egy domináns konformerük van. Megmutattuk, hogy a vízzel való komplexálás jelentős konformációváltozást eredményez, valamint kimutattuk a vizes a komplexekben az ún. kiralitás transzfer jelenségét. | Our results can be divided into two parts. Results on atmospherically or astrophysically relevant species belong to one group. Among these, alkoxy radicals have been identified as intermediates in matrix photolysis of alkyl-nitrites. Furthermore, the spectra of alkyl-peroxy radicals have been analyzed in US-Hungarian cooperation. These results can help the atmospheric monitoring of these species, and further kinetic measurements. Thiofulminic acid (HCNS), relevant both for astrophysicists and preparative chemists, has been prepared for the first time, together with its derivatives, e.g. FCNS. This is also the first measurement on the N-S stretching mode of a nitrile sulfide. Conformational analysis of model peptides constitutes the other group of our results. Conformational distribution of alfa- and beta-peptides have been analyzed by the aid of matrix isolation infrared (MI-IR) and matrix isolation vibrational dichroism (MI-VCD) spectroscopy. The latter has been developed and used by our group among the firsts. Besides many other results, it has been shown that although beta-peptides are more flexible than their alfa analogues, due to the strong H-bond their conformers are less evenly distributed. It has also been showed that complexation with water induces significant conformational change. The so-called chirality transfer phenomena has also been demonstrated in the water-peptide complexes

A bioszféra szerepe a légkör szén-dioxid tartalmának alakulásában = The role of the biosphere in the carbon dioxide budget of the atmosphere

A kutatási munkatervnek megfelelően a teljes kutatási időszakban folyamatosan mértük a hegyhátsáli mérőállomáson a CO2 koncentráció függőleges koncentráció-profilját és a régiót reprezentáló felszín-légkör szén-dioxid áramot. A mérőrendszert 2005 végén a mérőállomás közelében lévő kvázi-természetes gyep szén-dioxid forgalmának folyamatos mérésére alkalmas műszeregyüttessel egészítettük ki. 2006 elejétől folyamatosan mérjük a levegő metán, dinitrogén-oxid, kén-hexafluorid és szén-monoxid koncentrációját. Holland és amerikai együttműködésben eseti mintavétel alapján mértük a légköri szén-dioxid stabilizotóp-összetételét, és Európai Uniós támogatással a szén-dioxid függőleges koncentráció-profil méréseket nagy gyakoriságú (évi 80) repülőgépes mintavételekkel 3000 m-ig terjesztettük ki. Az adatok hozzáférhetők a nemzetközi kutatási programok számára. Megvizsgáltuk a koncentráció és a függőlege CO2-áram mérések területi reprezentativitását. Egyszerű box-modellt dolgoztunk ki a határrétegbeli koncentrációk időbeli menetének leírására, felhasználva a függőleges anyagáram méréseket, illetve a stabilizotóp-mérések eredményeit. A felszín és a légkör közötti szén-dioxid csere leírására adaptáltuk a Biome-BGC folyamatorientált ökológiai rendszer modellt, melynek segítségével megtettük az első kísérletet az országos léptékű bioszférikus CO2 mérleg meghatározására. Feldolgoztuk és kiértékeltük a hazai munkával, illetve amerikai kooperációban végzett nem-CO2 üvegházgáz méréseket. | In accordance with the workplan the vertical concentration profile of CO2 and the regional scale surface-atmosphere CO2 flux were continuously measured at Hegyhátsál. At the end of 2005 the monitoring system was completed by instrumentations measuring the surface-atmosphere CO2 budget of a semi-natural grassland located nearby to the station. Since the beginning of 2006 mixing ratios of methane, nitrous oxide, sulfur hexafluoride and carbon monoxide have also been monitored. In cooperation with American and Dutch partners the stable isotope composition of CO2 was also measured from occasionally taken air samples. The European Union supported the extension of the CO2 vertical concentration profiles up to 3000 m by means of frequent (80/year) aircraft soundings. The data are publicly available for the international research programs. The spatial representativeness of both the concentration measurements and the vertical flux measurements was studied. A simple box model was developed for the simulation of the temporal variation in the concentration of atmospheric trace constituents using the vertical flux and stable isotope concentration measurements. For the description of the surface-atmosphere CO2 exchange a process based ecological modell (Biome-BGC) was adapted. Using the model the first attempt was done to determine the biospheric carbon dioxide budget of Hungary. The available non-CO2 data were evaluated

Two-electron relativistic corrections to the potential energy surface, and vibration-rotation levels of water

Two-electron relativistic corrections to the ground-state electronic energy of water are determined as a function of geometry at over 300 points. The corrections include the two-electron Darwin term (D2) of the Coulomb–Pauli Hamiltonian, obtained at the cc-pVQZ CCSD(T) level of theory, as well as the Gaunt and Breit corrections, calculated perturbationally using four-component fully variational Dirac–Hartree–Fock (DHF) wavefunctions and two different basis sets. Based on the calculated energy points, fitted relativistic correction surfaces are constructed. These surfaces are used with a high-accuracy ab initio nonrelativistic Born–Oppenheimer (BO) potential energy hypersurface to calculate vibrational band origins and rotational term values for H216O. The calculations suggest that these two-electron relativistic corrections, which go beyond the usual kinetic relativistic effects and which have so far been neglected in rovibrational calculations on light many-electron molecular systems, have a substantial influence on the rotation–vibration levels of water. The three effects considered have markedly different characteristics for the stretching and bending levels, which often leads to fortuitous cancellation of errors. The effect of the Breit interaction on the rovibrational levels is intermediate between the effect of the kinetic relativistic correction and that of the one-electron Lamb-shift effect

Convergence of an s-wave calculation of the He ground state

The Configuration Interaction (CI) method using a large Laguerre basis restricted to l = 0 orbitals is applied to the calculation of the He ground state. The maximum number of orbitals included was 60. The numerical evidence suggests that the energy converges as Delta E^N approx A/N^(7/2) + B/N^(8/2) + >... where N is the number of Laguerre basis functions. The electron-electron delta-function expectation converges as Delta delta^N approx A/N^(5/2) + B/N^(6/2) + ... and the variational limit for the l = 0 basis is estimated as 0.1557637174(2) a_0^3. It was seen that extrapolation of the energy to the variational limit is dependent upon the basis dimension at which the exponent in the Laguerre basis was optimized. In effect, it may be best to choose a non-optimal exponent if one wishes to extrapolate to the variational limit. An investigation of the Natural Orbital asymptotics revealed the energy converged as Delta E^N approx A/N^6 + B/N^7 + ... while the electron-electron delta-function expectation converged as Delta delta^N approx A/N^4 + B/N^5 + >... . The asymptotics of expectation values other than the energy showed fluctuations that depended on whether $N$ was even or odd.Comment: 12 pages, 10 figures, revtex format, submitted to Int.J.Quantum Chemistr

Fém-ligandum kölcsönhatás vizsgálata gázfázisú molekulaspektroszkópiai módszerekkel = Investigation of transition metal complexes by gas phase molecular spectroscopic methods

- Új kvantumkémiai eljárást dolgoztunk ki az átmenetifém-származékok fotoelektron (pe) színképének értelmezéséhez. - UPS vizsgálatok alapján meghatároztuk a CS és CSe ligandumok CO-hoz viszonyított donor-akceptor sajátságát. - Előállítottuk a Co(CO)2(N | Novel quantumchemical method has been worked out for the interpretation of the photoelectron (pe) spectra of transition metal derivatives.-Donor-acceptor properties of CS and CSe related to CO have been determined on the basis of UPS investigations.-New compound of Co(CO)2(NO)(t-BuNC) has been prepared and investigated by HeI UPS and threshold PEPICO methods. From the PEPICO measurements energetic and thermochemical data were derived.-Trimethyl phosphane, -arsane, and –stibane derivatives of CpMnCO3 and CoCO3NO have been investigated by HeI and HeII UPS methods and conclusions were drawn concerning the ?-acceptor and ?-donor ability of the ligands.-A new series of isonitrile-substituted cobalt tricarbonyl nitrosyl (Co(CO)2(NO)CNR, R= Me, Et, nPr, iPr, nBu, nPe, CH2SiMe3) has been synthesized and studied by HeI UPS. The relative importance of electronic and steric effects of the isonitrile ligands, as a function of the size of group –R were determined. Metallocene ions (Cp2M+, M=Cr,Co,Ni) were studied by TPEPICO spectroscopy to investigate the mechanism, energetics and kinetics of the ionic dissociation processes.-Me3Si and Me3Ge radicals were generated by the gas phase thermolysis of (Me3Si/Ge)2Hg. The HeI pe spectra were recorded and assigned.-Electronic structure determination of precursors (diiodofuroxan and thiadiazoles) of some exotic molecules has been performed. Pyrolizer/ reactor directly attached to the pe spectrometer has been constructed

Interactions and Chemical Transformations of Coronene Inside and Outside Carbon Nanotubes

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures were prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π – π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor-phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes

MAPPING THE CONFORMATION SPACE OF α-PROLINE BY MATRIX-ISOLATION IR SPECTROSCOPY COMBINED WITH NIR LASER INDUCED CONFORMATIONAL CHANGE AND STATE-OF-THE-ART AB INITIO COMPUTATIONS

The conformers of $\alpha$-proline were studied by matrix-isolation IR spectroscopy. In order to group the vibrational bands to different conformers, conformational changes were induced by NIR laser irradiations, by exciting the OH stretching overtone of a selected conformer. For identification, the single conformer spectra were compared to state-of-the-art ab initio computations. Infrared spectra and anharmonic thermodynamic corrections have been computed by means of second order vibrational perturbation theory (VPT2), with GVPT2 and HDCPT2 models, respectively. A hybrid force-field was developed by addition of the cubic and semi-diagonal quartic B3LYP-D3/SNSD force constants to the (harmonic quadratic) B2PLYP-D3/maug-cc-pVTZ results. As the result of the spectrum analysis, seven conformers could be identified. Four of these conformers were present in the as-deposited matrix, two of them were generated by the NIR laser irradiation, and found to be stable in Ar matrix. The seventh conformer could also be produced upon the NIR laser irradiation, and it decays by H-atom tunneling to a lower energy form on the sub-second and minute timescales in Ar and N$_{2}$ matrices, respectively

Tunneling Lifetime of the ttc/VIp Conformer of Glycine in Low-Temperature Matrices

Conformer ttc/VIp of glycine and glycine-N,N,O-d(3) has been prepared in low-temperature Ar, Kr, Xe, and N-2 matrices by near-infrared (NIR) laser irradiation of the first OH stretching overtone of conformer ttt/Ip. Glycine (and glycine-N,N,O-d(3)) ttc/VIp was found to convert back to ttt/Ip in the dark by hydrogen-atom tunneling. The observed half-lives of ttc/VIp in Ar, Kr, and Xe matrices at 12 K were 4.4 +/- 1 s (50.0 +/- 1 h), 4.0 +/- 1 s (48.0 +/- 1 h), and 2.8 +/- 1 s (99.3 +/- 2 h), respectively. In correspondence with the observation for the cis-to-trans conversion of formic and acetic acid, the tunneling half-life of glycine ttc/VIp in a N-2 matrix is more than 3 orders of magnitude longer (6.69 X 10(3) and 1.33 X 10(4) s for two different sites) than in noble gas matrices due to complex formation with the host molecules. The present results are important to understand the lack of experimental observation of some computationally predicted conformers of glycine and other amino acids

Planetary nurseries: vortices formed at smooth viscosity transition

Excitation of Rossby wave instability and development of a large-scale vortex at the outer dead zone edge of protoplanetary discs is one of the leading theories that explains horseshoe-like brightness distribution in transition discs. Formation of such vortices requires a relatively sharp viscosity transition. Detailed modelling, however, indicates that viscosity transitions at the outer edge of the dead zone is relatively smooth. In this study, we present 2D global, non-isothermal, gas-dust coupled hydrodynamic simulations to investigate the possibility of vortex excitation at smooth viscosity transitions. Our models are based on a recently postulated scenario, wherein the recombination of charged particles on the surface of dust grains results in reduced ionisation fraction and in turn the turbulence due to magnetorotational instability. Thus, the alpha-parameter for the disc viscosity depends on the local dust-to-gas mass ratio. We found that the smooth viscosity transitions at the outer edge of the dead zone can become Rossby unstable and form vortices. A single large-scale vortex develops if the dust content of the disc is well coupled to the gas, however, multiple small-scale vortices ensue for the case of less coupled dust. As both type of vortices are trapped at the dead zone outer edge, they provide sufficient time for dust growth. The solid content collected by the vortices can exceed several hundred Earth masses, while the dust-to-gas density ratio within often exceeds unity. Thus, such vortices function as planetary nurseries within the disc, providing ideal sites for formation of planetesimals and eventually planetary systems.Comment: accepted for publication in MNRA