Search results for "Diss"

Pulsed photodissociation in an ion cyclotron resonance trap: extending the time range for unimolecular dissociation studies of metal clusters

1997

Dissociative charge transfer from highly excited Na Rydberg atoms to vibrationally excited Na2 molecules

2001

Abstract We report the observation of the vibrational dependence of dissociative charge transfer (DCT), Na2(X1Σg+, v″) + Na∗∗(nl) → Na− + Na + Na+, in a single Na/Na2 supersonic beam at low intrabeam collision energies (1.6 meV) using the STIRAP technique for selective vibrational excitation of Na2 in the electronic ground state and time-of-flight mass analysis of the ions. The efficiency of this process increases by about an order of magnitude in the range 13 ≤ v″ ≤ 22. Some perspectives are discussed regarding the implementation of a field-free ion-imaging technique for the detection of ions that will allow the direct determination of the kinetic energy distributions of product negative i…

Raman spectroscopy and crystal-field split rotational states of photoproducts CO and H2 after dissociation of formaldehyde in solid argon.

2012

Raman signal is monitored after 248 nm photodissociation of formaldehyde in solid Ar at temperatures of 9-30 K. Rotational transitions J = 2 ← 0 for para-H(2) fragments and J = 3 ← 1 for ortho-H(2) are observed as sharp peaks at 347.2 cm(-1) and 578.3 cm(-1), respectively, which both are accompanied by a broader shoulder band that shows a split structure. The rovibrational spectrum of CO fragments has transitions at 2136.5 cm(-1), 2138.3 cm(-1), 2139.9 cm(-1), and 2149 cm(-1). To explain the observations, we performed adiabatic rotational potential calculations to simulate the Raman spectrum. The simulations indicate that the splitting of rotational transitions is a site effect, where H(2) …

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

2008

This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO 2 (a-SiO 2 ). The most common form of interstitial oxygen species is oxygen molecule (O 2 ), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial 0 2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O 2 in long-range oxygen transport in a-SiO 2 ; formation of the Frenkel defect pair (Si-Si bond and interstitial oxygen atom, 0°) by dense electronic excitation; efficient photolysis of interstitial O 2 into O° with F 2 laser light (λ= 157…

Formation of HXeO in a xenon matrix: Indirect evidence of production, trapping, and mobility of XeO (1 1Σ+) in solid Xe

2004

IR spectroscopy, laser induced fluorescence (LIF), and thermoluminescence (TL) measurements have been combined to monitor trapping, thermal mobility, and reactions of oxygen atoms in solid xenon. HXeO and O(3) have been used as IR active species that probe the reactions of oxygen atoms. N(2)O and H(2)O have been used as precursors for oxygen atoms by photolysis at 193 nm. Upon annealing of matrices after photolysis, ozone forms at two different temperatures: at 18-24 K from close O ...O(2) pairs and at approximately 27 K due to global mobility of oxygen atoms. HXeO forms at approximately 30 K reliably at higher temperature than ozone. Both LIF and TL show activation of oxygen atoms around 3…

Contrasting evolution of iron phase composition in soils exposed to redox fluctuations

2018

Abstract Ferric iron (FeIII) solid phases serve many functions in soils and sediments, which include providing sorption sites for soil organic matter, nutrients, and pollutants. The reactivity of Fe solid phases depends on the mineral structure, including the overall crystallinity. In redox-active soils and sediments, repeated reductive dissolution with subsequent exposure to aqueous ferrous iron (Fe2+) and oxidative re-precipitation can alter Fe phase crystallinity and reactivity. However, the trajectory of Fe mineral transformation under redox fluctuations is unclear and has been reported to result in both increases and decreases in Fe phase crystallinity. Several factors such as water bu…

Bipolar membranes under forward and reverse bias conditions. Theory vs. experiment

1994

Abstract Bipolar membranes are layered structures composed of one cation-and one anion-exchange membrane joined together in series. The current—voltage curves of two recently developed bipolar membranes have been analysed theoretically and experimentally under both forward and reverse bias conditions. The experimental trends observed are high conductivity under forward bias conditions and high impedance first, and then electric field enhanced (EFE) water dissociation for high enough applied voltages, under reverse bias conditions. The forward bias measurements can contribute to a better knowledge of some of the transport parameters entering also in the reverse biased membrane. Comparison of…

Heterocyclic photorearrangements. Photoinduced rearrangements of 1,2,4-oxadiazoles substituted by an XYZ side chain sequence

1988

Photoinduced rearrangements of 1,2,4-oxadiazoles substituted by an XYZ side chain sequence at position 3 of the ring have been recognized. Examples taken out from previous results have been emphasized and some other patterns dealing with a 3-phenoxy and 3-enaminoketone sequence have been investigated. An intermediate species derived from photolysis of the ring O-N bond and characterized by a continuous 6π electron system involving the side chain sequence, was suggested to give ring closure to the rearrangement product.

Organoelement derivatives of steroids: synthesis and structural characterization of diorganotin chloride adducts of hormones

1986

Abstract Ten new diorganotin dichloride adducts of hormones of the type R 2 SnCl 2 ·2L [where R = Me, Et, n-Bu, Oct and Ph; L = 4-androsten-17s-ol-3-one ( A ); 5-androsten-3s-ol-17-one ( B ); 4-androsten-17α- methyl-17s-ol-3-one ( C ) and 3,17-dihydroxy-5- pregnene-20-one ( D )] have been prepared and characterized at 297 K and 223 K. Spectroscopic measurements (IR; Raman; 1 H, 13 C, 119 Sn NMR) suggest the dissociation or fast ligand exchange in solution at 297 K. Hexa-coordinated adducts with bonding through carbonyl oxygen and trans -R groups in octahedral geometry are formulated at 223 K.

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.