Ground-state Species Research Articles

Theoretical investigation involving electronic and vibrational calculations of the 2 2A1(3p)→1 2B2(3p) and the 3 2A1(4s)→1 2B2(3p) transitions in FH2 and FD2

Theoretical calculations have been carried out on the X 2A1, 1 2B2(3p), 2 2A1(3p), and 3 2A1(4s) electronic states of FH2. Equilibrium geometries and rotational constants as well as the first few vibrational levels of the excited states have been calculated, in order to obtain theoretical information on the 2 2A1(3p)→1 2B2(3p) and the 3 2A1(4s)→1 2B2(3p) transitions in FH2, which might be relevant to the observed spectra at about 7500 and 8000 Å. The results show that the equilibrium geometry of the first excited state of FH2, 1 2B2(3p), is quite different from those of the other excited states. The estimated transition energies (ΔE0) in FH2 are 1.68 and 1.97 eV for the transitions 2 2A1(3p)→1 2B2(3p) and 3 2A1(4s)→1 2B2(3p), respectively, while in FD2 the corresponding quantities are 1.65 and 1.95 eV, respectively. A search for a minimum on the ground state surface of FH2, which has been carried out near two saddle point geometries, has not found one. Thus the present calculations do not find a metastable ground state species.

The triple fluorescence of benzanilide and the dielectric medium modulation of its competitive excitation

The fluorescence of the benzanilide molecule at 298 K is inferred to consist of three independent electronic transitions associated with the single ground-state molecular species. F 1 (λ max340 nm), the normal fluorescence is observed weakly and is ascribed to an n,π*,-π,π* mixed state. F′ 2 is ascribed to the proton-transfer imidol tautomer fluorescence (previously reported) with unresolved λ max (inferred at ≈460 nm). F″ 2 is ascribed to a charge-transfer state fluorescence to the ground state, and occurs as a resolved CT transition in tetrahydrofuran at λ max 520 nm. Comparison of the spectra of N-methylbenzanilide exhibiting only F 1 and F″ 2 (CT) permitted the analysis of the benzanilide spectra.

Compounds of 3,4,7,9,9,14,16-Octamethyl- (and 7,9,9,14,14,16-Hexamethyl-3,4-diphenyl) 1,2,5,6,10,13-Hexaazacyclohexadeca-2,4,6,16-tetraene With Nickel(II) and Copper(II). Preparations and Kinetics of Acid Hydrolysis Reaction

The complex nickel(II) cation of the bis-diazine macrocycle 3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexadeca-2,4,6,16-tetraene, omht, is formed by reaction of the complex of 3,3,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone with butane-2,3-dione, and the complex of the 7,9,9,14,14,16-hexamethyl-3,4-diphenyl homologue, bzht, is similarly prepared by reaction with 1,2- diphenylethane-1,2-dione. The cation [Cu(hmtd)]2+ is formed by metal ion substitution for a precursor of the nickel(II) cation. Compounds of the nickel(II) cations occur as singlet ground state perchlorate salts, or as triplet ground state octahedral compounds with additional ligands, e.g. [Ni(omht)(NCS)2], [{Ni(omht)(N3)}2](ClO4)2 and [Ni(omht)(en)] (ClO4)2. The singlet ground state [Ni(omht)]2+ cation in dimethyl sulfoxide converts into a triplet ground state species with first-order rate constant of 2.1(2)×10-6 s-1 at 25°C, 5.1(2)×10-5 s-1 at 50°C. The cations are slowly hydrolysed by acid, and pseudo-first-order rate constants in 2 mol l-1 HCl/NaCl for hydrolysis of [Ni(omht)]2+ and [Cu(omht)]2+ at 25° and 50°C are reported. These are of the order of 10-5 (25°C), 10-4(50°C) s-1, with a non-linear dependence on [H+], and with the reactions faster for the nickel(II) cation.

High-Repetition-Rate Excimer-Based UV Laser Excitation Source Avoids Saturation in Resonance Raman Measurements of Tyrosinate and Pyrene

UV resonance Raman excitation using low-duty-cycle pulsed lasers such as the Nd:YAG can result in photophysical processes that interfere with Raman spectral studies of ground-state species due to the high incident laser energy fluxes. Depletion of the ground state occurs due to optical absorption and due to the population of intermediate levels which have lifetimes comparable to or longer than the excitation pulse width. In addition, formation of photochemical intermediates can occur. For example, excitation in resonance with the tyrosinate La electronic transition (∼240 nm) results in formation of tyrosyl radicals which deplete the concentration of ground-state tyrosinate molecules; as a result, decreased resonance Raman intensities are observed for vibrational modes of ground-state tyrosinate. For pyrene, excitation in resonance with the S4 electronic transition results in population of the long-lived S1 state via rapid internal conversion. This long-lived state bottlenecks relaxation back to the ground state, thus causing saturation of the ground-state pyrene Raman intensities. Given similar incident average laser powers and focusing conditions, higher-duty-cycle lasers result in decreased saturation. A comparison between a 20-Hz Nd:YAG and a 200-Hz excimer laser-based UV Raman excitation source demonstrates superiority of the excimer in avoiding both Raman saturation and interferences from photochemical transients. For the identical energy flux per pulse, the accompanying tenfold increase in average energy flux for the excimer, over the YAG, results in a dramatic improvement in the spectral signal-to-noise ratios. We report the first measurement of the absolute resonance Raman cross section of pyrene within the S4 transition. The Raman cross section of 48 barns/str measured for the 1632-cm−1 vibration with 240-nm excitation is the largest observed to date.

The solvolysis oftrans-[Co(4-Mepy)4Cl2]ClO4 in water: acetonitrile and water: dioxan mixtures

The solvolysis of the title complex is slower in 0 to 70% v/v aqueous dioxan than in aqueous acetonitrile at 40, 45, 50 and 55° C, a fact that is attributed to the higher basicity and ionizing power of the latter solvent mixtures. The observed non-linearity for logk (solvolysis) versus 1/D plots was interpreted in terms of the relative stability of ground and transition state species. The calculated Gibbs free energy for transfer of the species in the transition state is consistent with the extreme stretching of the chlorinecobalt bond, a result which confirms the interchange dissociative mechanismId for the complex under study.

Pyrrolo[1,4]benzodiazepine antitumor antibiotics: evidence for two forms of tomaymycin bound to DNA.

Tomaymycin is an antibiotic belonging to the pyrrolo[1,4]benzodiazepine group of antitumor compounds. Previous studies have shown that tomaymycin and other members of this group, which include anthramycin, sibiromycin, and the neothramycins, bind covalently through N-2 of guanine and lie within the minor groove of DNA. Two fluorescent ground-state species of tomaymycin were observed in protic solvents and on DNA. 1H NMR studies showed that the two fluorescent species in methanol are the 11R,11aS and 11S,11aS diastereomeric 11-methyl ethers of tomaymycin. On the basis of epimerization experiments and exchange of carbon-13 from 13CH3OH into the C-11 methoxy group of the tomaymycin methyl ether, a mechanism is proposed for their interconversion via 10,11-anhydrotomaymycin. Coupling information revealed that the solution conformations of the two diastereomers differ, with the C-5 carbonyl lying closer to the plane of the aromatic ring in the 11R,11aS diastereomer. The fluorescence excitation and emission spectra of the two emitting species in methanol were separated by time-resolved fluorescence spectroscopy and were associated with the diastereomeric forms identified by 1H NMR. Time-resolved fluorescence studies of tomaymycin in protic solvents and on DNA indicated that the absorption spectrum of the longer lifetime component (11R,11aS form) is red-shifted relative to the absorption spectrum of the shorter lifetime component (11S,11aS form), consistent with more extensive conjugation. The two conformational forms of tomaymycin on DNA were tentatively identified as the 11S,11aS and 11R,11aS diastereomeric adducts, which bind in opposite orientations in the minor groove. This proposal is supported by molecular modeling studies using a 6-mer duplex adduct of d(ATGCAT)2.

Potential energy surfaces for the molecular and free radical dissociations of H 2CS, F 2CS and Cl 2CS: An ab initio SCF MO study

Energies along the planar symmetric (C 2v) and planar assymetric (C s paths to molecular dissociation of the ground state thiocarbonyl halides, F 2CS and Cl 2CS, together with their transition state geometries, have been calculated by ab initio SCF MO methods using the STO-3G and 4-31G basis sets. For comparison, results on H 2CS at similar levels of calculation are also included in this report. In addition, the 4-31G ** basis set has been employed to predict the geometries of the ground state species and the endothermicities of their free radical dissociations. The results of experiments in which the lowest excited singlet states of these molecules have been photoexcited are interpreted in light of these calculations. Thermodynamic data for both molecular and free radical dissociations are evaluated and discussed.

Formation of highly charged ions of ambient gases near laser-heated targets.

The observation of spectral lines arising from ${\mathrm{Ne}}^{7+}$ ions in a 0.7-Torr atmosphere surrounding a laser-heated slab target is reported. Such line radiation is mainly emitted from a narrow zone which is located some distance away from the target, depending on the target material used (C, Li, or Al). According to a phenomenological model, the neon gas is initially heated to an electron temperature of ${k}_{B}$${T}_{e}$\ensuremath{\approxeq}200 eV and ionized to the ${\mathrm{Ne}}^{8+}$ (ground-state) species by supersonic radiative and electronic thermal conduction. The ${\mathrm{Ne}}^{7+}$-line radiation results in this model from three-body recombination of the ${\mathrm{Ne}}^{8+}$ plasma as it rapidly cools, following the cessation of the laser pulse and the overtaking by lower-temperature target plasma.

An atomic absorption study of ground state neutral atoms and ions in the inductively coupled plasma

Over the last few years the emission spatial structure of the inductively coupled plasma has been extensively mapped. However, for a more complete understanding of the plasma a detailed knowledge of both ground state and excited state species is required. In order to determine the ground state neutral atom and ion populations of the plasma a series of atomic absorption measurements have been carried out on the ICP. The atomic absorbance of neutral atom and ion lines of Ca, Mg and Cd have been measured as a function of plasma power and aerosol flow rate at one observation height. These data indicate that there is a large population of ground state ions for all these anarytes even at relatively low powers (< 1 kW).

LIF and OES detection of radical species in SiF 4 + H 2 plasmas

We have used laser-induced fluorescence (LIF) and optical emission spectroscopy (OES) to measure the relative concentrations of various radical species (in particular, SiF and HSiF) in glow-discharge plasmas of SiF 4 + H 2 used to deposit photovoltaic quality a-Si:H:F thin films. By varying the partial pressure ratio of SiF 4 versus H 2, we can qualitatively relate the concentrations of certain ground-state radical species (detected by LIF) and excited-state species (detected by OES) with the electronic properties of the deposited films.

The temperature-dependent red-shift of the visible absorption spectra of crystal violet in alcohol solutions

The visible absorption spectrum of the triphenylmethane dye, crystal violet, in various alcohol solutions at several temperatures has been recorded and subsequently analyzed by computer fitting. The observed spectral changes do not sustain either the earlier temperature-dependent absorption results of Lewis and co-workers or the concept of two ground-state species in equilibrium.

Synthesis and redox chemistry of octaethylporphyrin complexes of ruthenium(II) and ruthenium(III)

The syntheses and characterization of some new octaethylporphyrin complexes of ruthenium(II) and ruthenium(III) are described; the complexes are Ru(OEP)(P″Bu3)2, Ru(OEP)(CO)L (L = PPh3, P″Bu3), [Ru(OEP)(P″Bu3)2]Br, and Ru(OEP)(P″Bu3)Br, where OEP is the dianion of octaethylporphyrin. The Ru(OEP)(CO)EtOH complex, 1, which reversibly loses the ethanol ligand in CH2Cl2 solution, undergoes a one-equivalent oxidation at the porphyrin ligand to generate the cation-radical [Ru(OEP)•+(CO)]+; a purple species of 2A2u ground state, produced electrochemically in perchlorate media, can coordinate bromide to generate a green 2A1u ground state species that also results from oxidation of 1 using bromine. Coordination of pyridine to [Ru(OEP)•+(CO)]+ yields the Ru(OEP)•+(CO)py species that can also be formed by electrochemical oxidation of Ru(OEP)(CO)py. Addition of tertiary phosphines (PR3) to the cation-radical carbonyl species can lead to formation of [Ru(OEP)(PR3)2]+, via an internal electron transfer process from Ru(II) to the OEP•+ that appears to be triggered by loss of the CO ligand. A reversible one-electron electrochemical oxidation of Ru(OEP)(P″Bu3)2 at 0.03 V (vs. Ag/AgCl) in CH2Cl2 also gives the ruthenium(III) biphosphine cation, while a further one-electron oxidation at 1.2 V generates [Ru(OEP)•+(P″Bu3)2]2+, a ruthenium(III) π-cation radical characterized by esr. The [Ru(OEP)(P″Bu3)2]Br complex decomposes in the solid state to a mixture of Ru(OEP)(P″Bu3)Br, formed together with free phosphine via an intramolecular ligand exchange, and Ru(OEP)(P″Bu3)2, formed by reduction of the initial ionic ruthenium(III) cation with the phosphine that appears as [P″Bu3Br]Br.

Picosecond kinetics of radiationless relaxations of triphenyl methane dyes. Evidence for a rapid excited-state equilibrium between states of differing geometry

The photophysics of several triphenylmethane (TPM) dyes has been studied in n-alcohols and glycerol/water solutions. We have been able to measure the rate and characterize the viscosity dependence of several radiationless decay channels. We propose a kinetic scheme to account for our observations. Important points in this model are, the existence of more than one ground-state species (in some dyes), a rapid excited-state equilibrium between states of differing geometry and solvent-induced spectral shifts.

ChemInform Abstract: SOLVENT AND PH‐DEPENDENCE OF THE ABSORPTION AND FLUORESCENCE SPECTRA OF HARMAN: DETECTION OF THREE GROUND STATE AND FOUR EXCITED STATE SPECIES

Chemischer InformationsdienstVolume 13, Issue 36 Physical Organic Chemistry ChemInform Abstract: SOLVENT AND PH-DEPENDENCE OF THE ABSORPTION AND FLUORESCENCE SPECTRA OF HARMAN: DETECTION OF THREE GROUND STATE AND FOUR EXCITED STATE SPECIES O. S. WOLFBEIS, O. S. WOLFBEISSearch for more papers by this authorE. + FUERLINGER, E. + FUERLINGERSearch for more papers by this authorR. WINTERSTEIGER, R. WINTERSTEIGERSearch for more papers by this author O. S. WOLFBEIS, O. S. WOLFBEISSearch for more papers by this authorE. + FUERLINGER, E. + FUERLINGERSearch for more papers by this authorR. WINTERSTEIGER, R. WINTERSTEIGERSearch for more papers by this author First published: September 7, 1982 https://doi.org/10.1002/chin.198236050Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue36September 7, 1982 RelatedInformation

Photochemie substituierter Cycloheptatriene. XII. Dualfluoreszenz von 1‐Aryl‐4‐(p‐dimethylaminophenyl)‐cycloheptatrienen

Photochemistry of Substituted Cycloheptatrienes. XII. Dual Fluorescence of 1‐Aryl‐4‐(p‐dimethylaminophenyl)‐cycloheptatrienesDiarylcycloheptatrienes 1 in solution show two fluorescences originating from two different excited states. The ratio of intensities of the two fluorescences depends on the excitation energy. Two alternatives are discussed as the origin of the dual fluorescence: conformers in the ground state or an adiabatic photoreaction, respectively. The two emissions are ascribed to different geometries of the seven‐membered ring. Despite the different excitation spectra the dual fluorescence of the compounds 1 is explained as an excited state property of a single absorbing species, and not as two ground state species giving rise to the two fluorescence bands.

Photogeneration of very active homogeneous catalysts using laser light excitation of iron carbonyl precursors

Abstract : To summarize our main findings, we conclude that photolysis of Fe(CO)5 or Fe3(CO)12 yeidls an exceedingly active catalyst. The active catalyst is likely not an excited state species since the excited lifetimes of Fe(CO)5 or Fe3(CO)12 are too short to effect catalysis. The active species is likely an unsaturated ground state species photoproduced by loss of CO from Fe(CO)5 or Fe-Fe bond cleavage in Fe3(CO)12. Very high turnover rates for alkene isomerization and hydrosilation have been found. Moreover, very high turnover numbers (moles of product per mole of Fe initially present) are achieved. For example, when a single flash yields approximately 50% conversion of neat 1-pentene using approximately .01 m Fe(CO)5 the turnover number exceeds 400. Subsequent flashes yield an even greater extent conversion to ultimately completely equilibrate the linear pentenes. High light intensity does not appear to alter the product distribution where a number of products are possible (alkene + HSiEt3). The data show that very high light intensity can be used to produce product at a high observed rate and with high quantum efficiency (much greater than 1). (Author)

Magnetic circular dichroism study of porphyrin π cation radical species

Absorption and magnetic circular dichroism (MCD) spectra of selected metalloporphyrins and their bromine oxidized derivatives with bromide or perchlorate counter ions have been measured. The resultant data clearly discriminate between metal and porphyrin π ring oxidation. Further, in MCD spectrum is sensitive to the orbital ordering in the ground state of the π cation radical species formed from ZnTPP, CuOEP and CooEP. The [ZnTPP] +• Brt-, [ZnTPP] +• ClO − 4. [CuOEP] +• ClO − 4, and [Co(III)OEP] 2+ 2ClO − 4 species each of which has been assined a 2A 2u ground state, exhibit well-defined Faraday A terms under the B (Soret) band in the 400 nm region. In contrast, the data observed for [Co(III)OEP] 2+• 2Br −, a 2A 1u ground state species, does not have the A term character associated with the B band. Both classes of oxidized porphyrins exhibit an apparently charateristic series of weak, overlapping bands between 500 nm and 700 nm in the absorption and MCD spectra. The data show that this region of the MCD spectrum provides an assignment criterion for porphyrin π cation radical species.

ChemInform Abstract: STRUCTURE‐RESONANCE THEORY. A REVIEW OF APPLICATIONS TO Π‐HYDROCARBON SYSTEMS

Studies of structure-resonance theory applied to π-hydrocarbon systems are reviewed. The theory leads to quickly obtainable quantitative predictions of bond orders, charge distributions, and relative stabilities of ground state species or reaction intermediates. Numerical results correlate precisely with experimental properties, and with results of LCAO-MO-SCF calculations.

Evidence for ultrafast V–E transfer in boron oxide (BO)

Boron atoms react with oxygen (O2) and nitrous oxide (N2O) to yield the A 2Π–X 2Σ+ spectrum of BO. These reactions have been characterized from 10−5 to 10−3 Torr and at Ptotal ∼1 Torr in order to study relaxation and the rapid intramolecular V–E transfer BO(X 2Σ+, v″ =17)+X→BO(A 2Π1/2, v′=4)+X where X=O2, N2O, or a combination of these oxidants with argon. At the lowest pressures, a ground state boron atom interacts with a tenuous atmosphere of oxidant gas (beam–gas configuration). These ’’single collision’’ studies are extended in a controlled manner to higher pressure by entraining the metal atoms in argon and subsequently carrying out the oxidation of this mixture. At all pressures the measured A 2Π vibrational populations follow a markedly non-Boltzmann distribution. At pressures as low as 6×10−5 Torr, the formation of BO A 2Π1/2, v′=4 results from both the direct reaction B+RO→BO*+R and the collisional transfer BO(X 2Σ+)+RO→BO(A 2Π)+RO. The spin orbit interaction in BO connects rovibronic levels of X 2Σ+ and A 2Π1/2 facilitating a route for rapid intramolecular energy transfer. This energy transfer leads to the observation of sharp features in the neighborhood of the BO A 2Π–X 2Σ+ (4,0) band which may be correlated with the J′=18.5–21.5 perturbed rotational levels of BO(A 2Π1/2). We characterize this phenomenon determining population distributions, rotational temperatures, and the temperature dependence (boron source) of the chemiluminescence emission. The effects observed in BO demonstrate that a highly vibrationally excited ground state species interacts in the presence of a collision partner with a cross section substantially in excess of that expected for ’’gas kinetic’’ interaction. This behavior may have important implications for the modeling of energy systems as well as the ability to create population inversions requisite for the construction of visible chemical lasers.

Chemi-ionization in the metastable neon–metastable argon system

Studies were made by a merging-beams technique of the associative ionization (AI) reaction (1) Ne*+Ar*→NeAr++e and the Penning ionization (PI) reactions (2) Ne*+Ar*→Ne+Ar++e and (3) Ne*+Ar*→Ne++Ar+e. The relative kinetic energy of the reactants was varied from 0.01 to 10 eV. The Ne* and Ar* each represents a composite of the metastable 0P2,0 states. There is a complication in the present investigation which arises because AI and PI occur in collisions of Ne* with ground-state Ar. Since the reactant beams consist of metastable as well as ground-state species, the measurements are composites of chemi-ionization in both the Ne*–Ar* and Ne*–Ar systems. Information on AI and PI for the Ne*–Ar* system is obtained by subtracting from these composite measurements known contributions of the Ne*–Ar system. From such information it appears that the molecular states of the reactants are different for reactions (2) and (3).