Study in rare gas matrices

The proton transfer reaction has been also studied in rare gas matrices, showing some discrepancies with the gas phase (Brucker and Kelley 1989a,b Crepin and Tramer 1991) in 1- and 2-naphthol with ammonia, the AH B — A -HB + transition takes place for AH (NH3) /Ar matrix-embedded clusters with n > 3 (Brucker and Kelley 1989a,b). 

Persistent Re(CO)3(PR3)2 radicals have been spectroscopically and even crystallographically characterized, for example, Re(CO)3(PCy3)2 (5), suggesting the square-pyramidal structure to be the most favored one see Diffraction Methods in Inorganic Chemistry). Subcarbonyls hke Re(CO)2 have been studied in rare gas matrices. 

Knight, L. B., Kaup, J. G., Petzold, B., Ayyad, R., Ghanty, T. K., Davidson, E. R., 1999, Electron Spin Resonance Studies of 45Sc170, 89Y170, and 139La170 in Rare Gas Matrices Comparison With Ab Initio Electronic Structure and Nuclear Hyperfine Calculations , J. Chem. Phys., 110, 5658. 

The second part of this chapter focuses on actinide chemistry, where we start by describing some triatomic molecules containing a uranium atom, which have been studied both in the gas phase and in rare gas matrices. Most of actinide chemistry occurs, however, in solution, so we then describe actinide ions in solution. The extensive study of the multiple bond between two uranium atoms in the U2 molecule and in other diactinides is then reported. Finally, several examples of inorganic compounds that include U2 as a central unit are presented. 

Now concerning the fluorescence, while rare-gas atoms in rare-gas matrices do exhibit fluorescence (see the above reference of Schwentner et al.), NO is, to our knowledge, the sole molecule to exhibit Rydberg fluorescence in the condensed phase. That and the fact that NO has low-lying Rydberg states are the reasons we singled it out as our model system in this study. 

The half-life of 181W has been re-investigated and a value of 120.95 + 0.02 days determined, which differs significantly from the currently accepted value 272 The u.v. absorption spectra of molybdenum atoms isolated in rare-gas matrices at 14 K have been correlated with similar gas-phase spectral data and assigned in spherical symmetry. Diffusion of the metal atoms in an Ar matrix was also studied and some tentative evidence obtained for dimer formation.273 The standard heat of vapourization of molybdenum has been determined274 as 689.3 kJ (g atom)-1. 

Discussion. Copper in Krypton. The absorption spectra of copper atoms Isolated in rare gas matrices have been extensively studied (15-25) and the triplet of bands at 310nm attributed to a number of different causes. These include (1) spin orbit splitting and static axial site distortion (17), (2) multiple matrix sites (18), (3) exciplex formation between the metal and a single matrix atom (19), (4) long range metal-metal interactions (2 ), and (5) Jahn-Teller (JT) effect resulting from matrix cage atom vibrations on the excited metal (21,22,23). The MCD of Cu atoms in the rare gas matrices has recently been reported (24,25) and the results interpreted as consistent with either the distorted site or JT hypotheses (39). 

In view of the matrix-isolation infrared studies, the theoretical calculations, and those studies of aluminum beam-water reactions, it is of considerable interest to probe the electronic structure of aluminum metal atom hydration reaction intermediates and products Isolated in rare-gas matrices. Such a study will form a useful adjunct to the infrared research. A mapping of the electronic structure of these species will provide a data set to which further theoretical calculations may compare. A more focused elucidation of the nature of the gas-phase aluminum hydration reaction s chemiluminescent continuum emitter may be provided... 

Chemical Reactions. Products from gas-phase chemical reactions can also be trapped in rare gas matrices, and those products which absorb light can be studied by optical spectroscopic techniques. For example (31), the products from a low pressure 1 mm. of Hg) atomic flame of oxygen atoms plus acetylene were allowed to leak through a small oriflce in a borosilicate glass reaction chamber, where they were mixed with an excess of gaseous krypton at 1(H mm. of Hg pressure. The mixture was condensed on a quartz window cooled to liquid helium temperature. The only detectable small free radical found was HCO, but it was present in considerable quantities. Similar experiments by Harvey and Brown (23) showed that HNO could be easily produced and trapped from the gas-phase reaction of hydrogen atoms plus nitric oxide. 

Irradiation (X > 280 nm) of TCI in rare gas matrices produced different results (147). In this case IR spectral studies showed that the primary photoproducts are dlcarbonylcyclobuta-dieneiron and CO, which recombine upon warming the matrix ... 

There is a trend away from the study of particular molecules, such as benzene, which have been regarded as being examples of specific chromophore properties which are essential for a complete understanding of behaviour in more complex situations. Simple molecules are however still important subjects for research. The lifetimes of AgO molecules in rare gas matrices have been... 

A number of reports on phthalocyanines and porphyrins have been published. Spectral diffusion and thermal recovery of spectral holes burnt into phthalocyanine doped Shpol skii systems has been examined . An absorption, emission, and thermal lensing research on carboxylated zinc phthalocyanine shows the influence of dimerization on these properties. Fourier transformation of fluorescence and phosphorescence spectra of porphine in rare gas matrices has yielded much structural and electronic state data on this compound . Exciton splitting is an effect which is seen in the spectra of covalently linked porphyrins . A ps fluorescence study of the semirigid zinc porphyrin-viologen dyad has provided evidence for two dyad conformers . Spectral diffusion in organic glasses has been measured by observing the hole recovery kinetics over the time scale of 1 to 500 ms for zinc tetrabenzoporphyrin in PMMA . 

Rotational tunneling of partially deuterated methane in rare gas matrices and adsorbed on surfaces has been studied in detail by neutron scattering... 

The most intensely studied species are the group 6 pentacarbonyls, M(CO)5(H2), which have been observed in rare-gas matrices, in liquid Xe solutions at - 70°C (a very useful medium), in alkane solvents, and in the gas phase. Perhaps the most novel preparation is photolysis of the hexacarbonyls impregnated in polyethylene disks under H2 or N2 pressures to give M(CO)6 n(L)n, where n = 1,2 for L = H2 and 1-4 for N2.175 Reactivity follows the order Mo > Cr > W, and H2can displace coordinated N2 in the polyethylene systems. In all media, vibrational spectroscopy provides evidence for H2 rather than dihydride binding, and the H-H, H-D, and... 

In this section we report some theoretical work on the molecular spectroscopy in rare gas matrices. Due to the difficulty in modelling the environment, theoretical studies for a long time compared the results obtained from gas phase calculations with experimental data in matrices. However, it has been demonstrated that the effect of the matrix is not negligible, and may strongly depend on the rare gas, as discussed recently by Li et al [186]. Even if relativistic pseudopotentials lead to a substantial reduction of computational costs, one still needs to treat explicitly a certain number of valence electrons, for instance eight electrons for each rare gas (Rg) atom. A further simplification is to consider a rare gas atom as a zero-electron system with all its electrons in the core represented by the so-called zero-electron pseudopotential or e-Rg pseudopotential (for further details see Grofi and Spiegelmaim [187,188] and references therein). As... 

The rare gas matrix isolation technique has been successfully used to study reactive intermediates generated by both chemical and physical methods -. In this report vve extend the utility of the matrix isolation technique by demonstrating that chemistry may be initiated in molecular systems isolated in rare gas matrices using electron beams with an accelerating voltage of 25 kV. 

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