Transient Absorption Features Research Articles

Photochemical behavior of phosphorus ligands-substituted diamanganase carbonyls

Photochemistry of ax,ax-L(OC) 4Mn-Mn(Co) 4L (L=P(n-Bu) 3) (S) in cyclohexane has been studied by means of laser photolysis with a uv-vis detection system. In addition to the transient absorption features due to the occurrence of primary processes, (1) Mn-Mn bond cleavage to give (Mn(CO) 4L (I), and 2) CO dissociation without metal-metal bond cleavage to give Mn 2(CO) 7L 2 (II). Two absorption features are observed: The one is attributed to the formation of a secondary intermediate (IV), whose structure is assigned to ax,eq-L(OC) 4Mn-Mn(CO) 4L, from the reaction of II with CO. The other appears to show the possibility of a third primary process (3) in the photolysis system of the disubstituted L(OC) 4Mn-Mn(CO) 4L. A whole photochemical reaction scheme is proposed in Scheme 2 and the nature of the intermediates, IV and unknown II is discussed.

Intramolecular electron transfer in the reductive chromophore-quencher complex [(bpy)Re(CO)3(py-PTZ)

Three metal complexes containing the reductive quencher ligand py-PTZ, ((bpy)Re(CO)/sub 3/(py-PTZ))/sup +/ and ((bpy)/sub 2/Ru/sup II/L(py-PTZ))/sup n+/ (where L = Cl/sup -/ (n = 1), PTZ = phenothiazine and acetonitrile ( n = 2)), were prepared and their redox and spectral properties investigated. The chromophore-quencher complex have essentially the same photophysical properties as their corresponding pyridine analogues at 77K in a 4:1 (v/v)) ethanol/methanol glass, but their properties are profoundly different in fluid solution. For the Re complex in fluid solution excitation of the Re..-->.. ..pi..*(bpy) metal to ligand charge-transfer (MLCT) chromophore at 355 nm is followed by rapid (<10 ns) appearance of transient absorption (TA) features at 350 and 500 nm consistent with formation of the charge-separated state ((bpy/sup.-/)Re(CO)/sub 3/(py-PTZ/sup.+))/sup +*/. Picosecond TA experiments monitored at 500 nm show that the PTZ/sup .+/ site grows in within approx.200 ps in polar organic solvents following laser excitation at 355 nm. The transient behavior observed leads to the conclusion that initial excitation of the MLCT chromophore is followed by rapid intramolecular electron-transfer quenching with k/sub q/(RT) = 4.8 x 10/sup 9/ s /sup -1/ in acetonitrile to give the charge-separated excited state ((bpy/sup .-)Re(CO)/sub 3/(py-PTZ/sup.+))/sup +/, which, in turn, decays tomore » the ground state with k/sub 2/ = 4.0 x 10/sup 7/ s/sup -1/. 36 references, 11 figures, 2 tables.« less

Picosecond spectroscopic studies of (d8-d8) binuclear rhodium and iridium complexes: a comparison of 1B2 and 3B2 reactivity in bis(1,5-cyclooctadiene)bis(.mu.-pyrazolyl)diiridium(I)

Picosecond transient kinetics and difference spectra have been recorded for the singlet and triplet (dsigma*psigma) excited states in the d/sup 8/-d/sup 8/ dimers Rh/sub 2/(TMB)/sub 4//sup 2 +/ (TMB = 2,5-dimethyl-2,5-diisocyanohexane) and (Ir(..mu..-pz)(COD))/sub 2/ (pz = pyrazolyl, COD = 1,5-cyclooctadiene). The singlet excited state in the rhodium dimer (tau=- 820 ps) displays a strong transient absorption feature maximizing at 440 nm that is not present in the spectrum of the triplet excited state. This intense absorption feature, characteristic of a /sup 1/(dsigma-psigma) electronic configuration, is assigned to a /sup 1/(dsigma*psigma) ..-->.. /sup 1/(psigma/sup 2/) excitation. This singlet excited state lifetime of the iridium dimer in cyclohexane is less than 20 ps. Though the solvent 1,2-dichloroethane (DCE) quenches luminescence from both singlet and triplet excited states in (Ir(..mu..-pz)(COD))/sub 2/ and oxidatively adds to the dimer upon steady-state illumination, picosecond spectroscopy finds no evidence for any chemical reactivity of the very short-lived singlet excited state. The quenching of (Ir(..mu..-pz)(COD))/sub 2/ singlet luminescence in DCE appears to result from enhanced singlet ..-->.. triplet intersystem crossing in DCE relative to that in cyclohexane. Also, the invariance of triplet yield in these two solvents indicates that the efficiency of intersystem crossing is near unity.

Site of attack in the interaction of hydrated electrons and hydroxy radicals in the pulse radiolysis of arylalkylamines in aqueous solutions

The site of attack and the reaction rate constants of e - aq with various alkylarylaminesbenzylamine, α-methyl benzylamine, aminodiphenyl methane, N-methylbenzylamine, and N,N-dimethylbenzylamine have been determined by pulse radiolysis at different pH values taking into consideration the ionization constants of the amino group present in these molecules. The k values are influenced by the polar and steric effects brought out by the substituents and decrease with deprotonation of the NH + 3 group. Reductive deamination is the major observation when the amino group is protonated while the molecule with unprotonated amino group forms a radical anion by the addition of e - aq to the aromatic nucleus. From the characteristic transient absorption spectra and extinction coefficients of the deaminated radicals, the extent of deamination is calculated. The ȮH radicals do not lead to any oxidative deamination nor abstract α-H atom, but only add to the aromatic ring. The kȮH+arylalkylamines are estimated to be in the range 5.2 to 6.9 × 10 9 M -1 s -1. On the other hand, the O - radicals give rise to substituted benzyl radical by the abstraction of α-H atoms from the aliphatic chain.

Infrared light curves of Type I supernovae

view Abstract Citations (105) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared light curves of type I supernovae. Elias, J. H. ; Frogel, J. A. ; Hackwell, J. A. ; Persson, S. E. Abstract The paper presents observations of two Type I supernovas in NGC 1316 and one in NGC 4536 at J, H, and K, which provide the best available Type I supernova light curves at these wavelengths. The light curves are characterized by a double maximum, with the effect strongest at J due to the development of a transient absorption feature during the intervening minimum. The dispersion of the three sets of light curves in absolute magnitude is less than the uncertainty in relative distances of the supernovas, indicating that infrared light curves of supernovas may be useful as distance indicators within a few tens of Mpc. Publication: The Astrophysical Journal Pub Date: December 1981 DOI: 10.1086/183683 Bibcode: 1981ApJ...251L..13E Keywords: Infrared Astronomy; Light Curve; Stellar Magnitude; Supernovae; Stellar Envelopes; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products NED (3) SIMBAD (1)

Application of Pulse Radiolysis to Biological Macromolecules

The present article outlines the recent development of pulse radiolysis studies on aqueous solutions of enzyme proteins.Pulse radiolysis method has provided much information on fast process induced by a short-lived perturbation of various substances. In recent few years, the results from an application of the method to aqueous solutions of biological macromolecules have been increasingly accumulated. Particularly an extensive work on enzyme proteins reveals that protein molecule reacts with the primary radicals produced in radiolysis of water to give a characteristic transient absorption and above 1010M-1sec-1 is determined as a rate constant for the reaction. Studies on selective reactions of inorganic radical anions with proteins suggest that radiation chemical technique could provide a new method for investigation of molecular nature of biological substances. Finally the reactivity of protein towards OH radicals is discussed in terms of tertiary structure of the protein molecule.