Excited Doublet States Research Articles

Symmetry breaking in radicals: NO 2, NS 2 and NO 3

The coupled-cluster method with single and double excitations is used to investigate the equilibrium configuration of the ground and two excited doublet states of the NO 2, NS 2 and NO 3 radicals. The ground 2A 1 and excited 2B 2 states of NO 2 have C 2v symmetry, whereas the C s minimum of the 2A 2 state is too close (less than 10 cm −1) to the lowest C 2v energy to draw firm conclusions. NS 2 shows C 2v symmetry for the same three states. The ground 2B 2 state of NO 3 has D 3h symmetry, but the excited 2E state splits with symmetry breaking.

Electronic structure and photobehavior of hexaamminechromium (III) ion

The electronic structures of the hexaamminechromium (III) ion [Cr(NH 3) 6] 3+ in its quartet ground state and in its lower excited quartet and doublet states have been investigated through theoretical models based upon a combination of MS-LSD, LCGTO-LSD and ligand-field procedures. The calculations have been carried out in the contexts of O h and D 4h microsymmetries, the latter being applicable to consideration of the first quartet excited state, which is known from experiment to undergo distortion to a tetragonal geometry. The calculated results in conjunction with spectroscopic findings have provided new insight into examining the photobehavior of this complex ion with specific reference to internal conversion between lower excited quartet states, promoted by spin-orbit interaction, and to the potential involvement of a back intersystem crossing from the lowest excited doublet state [ 2E g(O h)] to the lowest excited quartet [ 4E g(D 4h)].

Excited states of NiH and NiD in the 15 500–19 000 cm −1 region: Rotational analysis with the aid of laser-induced fluorescence spectroscopy

The first vibrational and rotational analysis is reported for three previously unknown states in NiH in the energy region 15 500 to 19 000 cm −1. New information about known excited electronic states in this region is also presented. The new states were found in absorption and emission spectra and also in cw laser fluorescence excitation spectra of NiH and NiD. Compared to the group of low-lying states in NiH ( T < 5000 cm −1) which was reported previously, the density of the vibronic levels from the upper group of states is much higher. However, unambiguous vibrational numbering assignments in the optical spectrum could be obtained based on the observed splittings due to different nickel isotopes and the energy differences between some NiH and NiD bands. The following new labels are given to the upper states to preserve previous lettering and to indicate the Ω value: A2.5 (formerly A 2 Δ 5 2 ), B2.5 (formerly B 2 Δ 5 2 ), D1.5 (formerly 2 Δ 3 2 , E1.5 (new), F3.5 (formerly 2 Φ 7 2 ), I1.5 (new), and G2.5 (new). From the structure of several bands and the Zeeman patterns of a few lines, a clear relationship is emerging for excited doublet states in NiH arising from the Ni + 3 d 84 s 2 F parent. Magnitude of Ω-doublings , consistent vibrational intervals, ΔG 1 2 , and expected spin-orbit interactions link the various substates in this group although a Hund's case (a) picture is not adequate to describe the severely mixed character of these states. There is also some evidence that the A2.5 state and possibly the E1.5 state have dominant quartet rather than doublet character.

Ab initio study of some doublet excited states of AlH 2

Ab initio unrestricted Hartree-Fock (UHF) calculations were carried out with a relatively large basis set in order to search for the equilibrium geometries of eight doublet electronic states of the AlH 2 radical. The results indicate that among these eight states there are three unstable states and one Rydberg state. The predicted equilibrium geometries for the X 2 A 1 and 2 B 1 states are in good agreement with the available experimental and configuration interaction (CI) results. The vibrational frequencies in the five stable states were calculated under the assumptions of valence forces. On the basis of the energetic results, some qualitative predictions about the electronic spectra of AlH 2 are also presented.

Excited-state properties of Escherichia coli DNA photolyase in the picosecond to millisecond time scale

Escherichia coli DNA photolyase contains a stable flavin radical that is readily photoreduced in the presence of added electron donors. Picosecond, nanosecond, and conventional flash photolysis technique have been employed to investigate the events leading to photoreduction from 40 ps to tens of milliseconds following flash excitation. Direct light absorption by the flavin radical produces the first excited doublet state which undergoes rapid (within 100 ps) intersystem crossing to yield the lowest excited quartet (n pi*) state. In contrast, light absorption by the folate chromophore produces a new intermediate state via interaction of the folate excited singlet state with the ground-state flavin radical, leading to an enhanced yield of the excited radical doublet state and hence quartet state. Subsequent reaction of the excited quartet state involves hydrogen atom abstraction from a tryptophan residue. Secondary electron transfer from added electron donors occurs to the oxidized tryptophan radical with rate constants ranging from 10(4) (dithiothreitol) to 4 x 10(6) M-1 s-1 (n-propyl gallate). The low value of the latter rate compared to reduction of the tryptophan radical in lysozyme suggests that the reactive tryptophan is highly buried in photolyase. A redox potential diagram has been constructed for the ground and excited states involved. It is concluded that the one-electron reduction potential of the excited quartet state of the flavin radical must be at least 1.23 V more positive than the ground state, in agreement with the value of delta E greater than 1.77 V calculated from spectroscopic data.

Electron transfer to excited doublet states. Photoirradiation of 10-methylphenothiazine cation radical perchlorate in solutions of phenylacetylene and p-tolylacetylene in acetonitrile

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron transfer to excited doublet states. Photoirradiation of 10-methylphenothiazine cation radical perchlorate in solutions of phenylacetylene and p-tolylacetylene in acetonitrileHenry J. Shine and Da Chuan ZhaoCite this: J. Org. Chem. 1990, 55, 13, 4086–4089Publication Date (Print):June 1, 1990Publication History Published online1 May 2002Published inissue 1 June 1990https://doi.org/10.1021/jo00300a026RIGHTS & PERMISSIONSArticle Views357Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (539 KB) Get e-Alerts Get e-Alerts

Ammonia activation by scandium(1+) and titanium(1+): electronic and translational energy dependence

The reactions of Sc' and Ti' with ammonia are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. The effect of electronic energy for the Ti+ reactions is also probed by varying the conditions for forming Ti+. Excited doublet states of Ti' are found to be much more reactive than the a4F ground and b4F first excited states. Both metals form the MH+, MNH', and MNH2+ products, while only Ti+ forms MN+. The results are consistent with reaction that occurs primarily through a covalently bound insertion intermediate, H-M+-NHz, having a singlet and doublet spin state for M = Sc and Ti, respectively. The reactivities of the different electronic states of the reactant ions can be explained by using spin conservation concepts. The thresholds for the cross sections of the endothermic reactions are interpreted to give the 298 K bond energies of Do(Sc+-NH2) = 3.69 i 0.07 eV, Do(Sc+-NH) = 5.16 f 0.10 eV, Do(Ti+-NH2) = 3.69 f 0.13 eV, D(Ti+-NH) = 4.83 f 0.12 eV, and Do(Ti+-N) = 5.19 f 0.13 eV. The large bond strengths of the M+-NH2 and M+-NH species indicate that the lone pair electrons on the nitrogen atom are involved in the metal-ligand bond.

Photochemical water exchange in chromium(III) complexes, and mechanism of solvent assisted excited state deactivation

Abstract

Potential energy surfaces for Tc+H2 and Ru+H2 reactions

Potential energy surfaces of 12 electronic states of TcH2 and RuH2 are obtained using a complete active space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction calculations (MRSDCI). The 6S ground state of Tc has to surmount a barrier of 40 kcal/mol to insert into H2 while the 5F ground state of Ru inserts into H2 with a much smaller barrier of 8.5 kcal/mol. The excited 6D, 4D, and doublet states of Tc atom insert into H2 spontaneously. The ground state of TcH2 is a linear 6Σ+g state arising from the 6S state of the Tc atom, while the ground state of RuH2 is of bent equilibrium geometry with 3A2 symmetry. A nearly degenerate bent state of 3B1 symmetry also exists for RuH2 . The bent minima of TcH2 are at least 0.9 eV above the linear 6Σ+g ground state of TcH2 . The ground state of RuH2 is 35 kcal/mol more stable than Ru(3F) + H2 while the 6Σ+g ground state of TcH2 is 27 kcal/mol more stable than Tc(6S)+H2 . All the bent states of TcH2 and RuH2 are ionic exhibiting strong M+H− polar bonds. The M–H bonds are made of dsp hybrid bonds as evidenced from Mulliken population analyses.

Simulation of magnetic moments in a dilute induced-moment Heisenberg magnet

The author considers a diamagnetically diluted induced-moment Heisenberg magnet in which the active sites have a singlet electronic ground state and an excited doublet state. Moments may be induced at the active sites by mixing the doublet into the singlet through a magnetic exchange interaction or an external magnetic field Hz applied parallel to the z direction. The single-ion Hamiltonian describing this system is -H= Sigma ijJijSiSj- Delta Sigma i(Siz)2-Hz Sigma iSiz, where Delta is the single-doublet separation. Using self-consistent mean-field calculations on computer-generated lattices in one, two and three dimensions, and with connectivities z=2, 3, 4, 6 and 8, he studies the distribution of moments at T=0 as a function of the concentration of diamagnetic impurities, the ratio Jij/ Delta and H. When Hz=0, diamagnetic atoms rapidly reduce the value of the mean induced moment, leaving moments of significant size only in regions composed of active sites that are completely surrounded by other active sites. The sensitivity of the lattice towards dilution increases as z increases. The application of Hz compensates to some extent for the effect of the diamagnetic impurities, raising the mean-moment and reducing the variance of the distribution of the size of individual moments.

MINDO/3 CI Study of NCO Spectrum and the Chemiluminescent Reaction N + CO → NCO + h

Abstract The mechanism of chemiluminescence in the reaction N + CO → NCO (1) and the electronic spectrum of NCO radical have been investigated by means of MINDO/3 CI method. The potential energy curves for the ground and some excited doublet and quartet states have been built along the linear and nonlinear (angle NCO is equal to 150°) reaction coordinates. The reaction channels N(4S) + CO(1σ+), N(2D) + CO(1°+) and N(2P) + CO(1σ+) have been discussed in detail. The spin-orbit coupling (SOC) constants for 2π states and nonadiabatic SOC matrix elements <4σ−|;HSOC|X2π> have been calculated.

Quenching of the doublet excited state of tris(polypyridine)chromium(III) ions by oxalate ions: an example of irreversible electron transfer

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuenching of the doublet excited state of tris(polypyridine)chromium(III) ions by oxalate ions: an example of irreversible electron transferCarl R. Steffan, Andreja Bakac, and James H. EspensonCite this: Inorg. Chem. 1989, 28, 15, 2992–2995Publication Date (Print):July 1, 1989Publication History Published online1 May 2002Published inissue 1 July 1989https://doi.org/10.1021/ic00314a023RIGHTS & PERMISSIONSArticle Views52Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (488 KB) Get e-Alerts Get e-Alerts

Perturbations of the low-energy doublet excited state of chromium(III). Competing heavy-atom and macrocyclic ligand effects in thermally activated relaxation pathways

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPerturbations of the low-energy doublet excited state of chromium(III). Competing heavy-atom and macrocyclic ligand effects in thermally activated relaxation pathwaysRonald B. Lessard, John F. Endicott, Marc W. Perkovic, and L. A. OchrymowyczCite this: Inorg. Chem. 1989, 28, 13, 2574–2583Publication Date (Print):June 1, 1989Publication History Published online1 May 2002Published inissue 1 June 1989https://doi.org/10.1021/ic00312a015RIGHTS & PERMISSIONSArticle Views142Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Quenching of excited doublet states of organic radicals by stable radicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuenching of excited doublet states of organic radicals by stable radicalsA. Samanta, K. Bhattacharyya, P. K. Das, P. V. Kamat, D. Weir, and G. L. HugCite this: J. Phys. Chem. 1989, 93, 9, 3651–3656Publication Date (Print):May 1, 1989Publication History Published online1 May 2002Published inissue 1 May 1989https://doi.org/10.1021/j100346a055RIGHTS & PERMISSIONSArticle Views293Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (781 KB) Get e-Alerts

Fluorescence of the benzophenone ketyl radical: solvent effects

The fluorescence of the benzophenone kethyl radical (BKR) was studied in different solvents by a double-pulse excitation technique using two synchronized lasers. Fluorescence quantum yields of the BKR were determined employing a new technique suitable for measurement of short-lived transients with low level emission. By analysing the fluorescence spectral shape and the values of the quantum yields in the different solvents it can be concluded that charge transfer complexes are formed in the excited doublet state of BKR, with the molecules of the solvents exibiting electron-donor properties.

ChemInform Abstract: Lifetime and Electronic Spectra of p‐Methoxybenzyl Radical in the Lowest Excited Doublet State in Solution

ChemInform Abstract: Lifetime and Electronic Spectra of p‐Methoxybenzyl Radical in the Lowest Excited Doublet State in Solution

Energy level assignments in Ni XVI

The beam-foil spectrum of nickel at 28 MeV has been analyzed in the grazing-incidence region. 41 transitions have been assigned between excited doublet states in the ( n = 3) array of Ni XVI, yielding the energies of the 16 doublet levels belonging to the 3p 3 and 3s3p3d configurations.

Study of 3d ? 4f and 3d ? 5f quartet and doublet transitions of doubly excited three-electron ions

We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, O VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDF calculations along the isoelectronic sequence. The same method also led to the identification of two 3d – 4f quartet transitions in Mg X.

Lifetime and electronic spectra of p-methoxybenzyl radical in the lowest excited doublet state in solution

Observation des spectres d'absorption D n ←D 1 et de fluorescence D 1 →D 0 de l'etat doublet excite le plus bas du radical p-methoxybenzyle. Confirmation d'une duree de vie longue a temperature ambiante et d'une relaxation non radiative dependant faiblement de la temperature. La relaxation semble due a la rotation du groupe methoxy

Mean-field model of the Verwey transition in magnetite.

A mean-field model is applied to the Verwey transition in ${\mathrm{Fe}}_{3(1\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}})}$${\mathrm{O}}_{4}$. Parametrization of the internal energy, in terms of the experimental dependence of transition temperature on metal-oxygen nonstoichiometry, yields results consistent with the existence of two regimes on either side of a critical composition ${\ensuremath{\delta}}_{c}$=0.0039. For \ensuremath{\delta}${\ensuremath{\delta}}_{c}$, first-order transitions occur, with singlet ground states and doublet excited states. For \ensuremath{\delta}g${\ensuremath{\delta}}_{c}$, second-order transitions result, for ground and excited states of equal degeneracy. The density of states, determined by a single long-range-order parameter is used to calculate the Fermi potential of a free-electron gas and associated electrical transport properties, as a function of temperature and nonstoichiometry. The canonical cusp catastrophe describes critical behavior in the mean-field approximation.