Ultrafast intersystem crossing in 9,10-anthraquinones and intramolecular charge separation in an anthraquinone-based dyad

Femtosecond transient absorption spectroscopy was employed to determine quantitatively the ultrafast S1-T1 intersystem crossing in a 2-substituted 9,10-anthraquinone derivative (3), kisc = 2.5 x 10(12) s-1. Notwithstanding this rapid process, photoexcitation of dyad 1 is followed by competition between intersystem crossing and intramolecular charge separation, the latter leading to a short-lived (2 ps) singlet charge-transfer (CT) state. The local triplet state itself undergoes slower charge separation to populate a relatively long-lived (130 ns) triplet CT state. An earlier report about the formation of an extremely long-lived CT state (> 900 micros) in 1 was found to be erroneous and was related to the sacrificial photo-oxidation of the dimethylsulfoxide solvent used in that study. Finally, some important criteria have been formulated for future experimental validation of "unusually long-lived" CT states.     

1,2,4-Triazole complexes,part X. Complexes of transition metal(II) cyanates and thiocyanates with 1-phenyl-1,2,4-triazole

Summary Complex formation of transition metal(II) cyanates and thiocyanates (Z) with 1-phenyl-I,2,4-triazole (1-PhTr) is described. An assignment of the i.r. spectra of free and coordinated 1-phenyl-1,2,4-triazole is given. The products are mononuclear M(1-PhTr)₄Z₁ and polvnuclear M(1-PhTr)₂Z₂ compounds. The former occur ascis andtrans isomers; the latter include bridging (thio)cvanates. A tetrahedral coordination is found for zinc complexes.Part IX, D. W. Engelfriet, G. C. Verschoor and W. den Brinker, to be published.     

A systematic investigation of ionization occurring in few electron collision systems: H0, He0 impact on He

Absolute doubly differential cross sections for electron emission occurring in fast (0.5 MeV/amu) H⁰ — and He⁰ — He collisions have been measured using standard non-coincidence techniques as well as emitted electron — charge state analysed projectile coincidence techniques. The comparison of these data with results obtained for H⁺ and He⁺ impact provides insight into the influence of one or two loosely bound projectile electrons on the probabilities for projectile, target, and simultaneous projectile — target ionization. PWBA calculations for these systems demonstrate good agreement with the experimental data for target and projectile ionization and indicate the importance of including simultaneous ionization processes in the theoretical treatment.     

K-Ionization probability across the 460-keV12C(p,p 0) resonance

We have remeasured theK-shell vacancy production probabilityP _K across the 460-keV¹²C(p, p ₀) resonance, previously investigated by Duinker et al. We are unable to confirm the large (～70 %) variation ofP _K across the resonance, found by Duinker et al. for protons elastically scattered at 125°. Our values for the ratioP _K (142°)/P _K (16°) are independent (within±20%) of the proton bombarding energy over the resonance region, in agreement with theoretical predictions by Blair and Anholt, Feagin and Kocbach, McVoy and Weidenmüller. Our average value for this ratio, equal to 0.88 ±0.06, agrees with the value 0.88 calculated by Amundsen and Aashamar.     

Possible evidence for heavy-ion-induced collective electron emission from solids

A peak has been observed for the first time in the angular distributions of low energy electrons (E_c<5 eV) emitted under heavy-ion bombardment of solids. The peak energy and angle coincide with the peak energy and angle predicted recently for collective electron emission in heavy-ion-solid collisions.     

TotalK-vacancy production in Ne (10 MeV) traversing Al

Deexcitation of projectile inner shell vacancies created while traversing a solid foil may take place via competing processes: a) vacancy sharing with foil atoms in close impacts, b) radiative and non-radiative electron capture, and c) such X-ray and Auger electron transitions as are possible in the heavy ion projectile. The change inK-vacancy creation with foil thickness can be investigated by measuring either projectile or target X-rays where the vacancies are created by Coulomb excitation and processa. In the system Ne (10 MeV) on Al, detecting AlK X-rays, the NeK-vacancy production probability has been determined.     

Studies of neonL-shell excitation by impact of highly ionized heavy ions

Passage of foil-excited 1.4 MeV/A S and 1.1 MeV/A Cl ions of neon charge state ～ 12⁺ through neon gas targets at pressure ～100 mTorr has been found to be accompanied by copious production of Ne II–VIII excited states. Comparable excitation cross-sections ～10^?18 cm² are found for a large number of levels belonging to all of these charge states and corresponding to principal quantum numbersn=2, 3, 4. Vacancy distributions very similar to those found in beam-foil excitation of ～1MeV neon beams are found. Because the Ne recoil velocities are small compared to the fast beam velocities characteristic of the beam-foil source, it is possible to reduce both Doppler shifts and spreads by 3–4 order of magnitude for equivalent collimation. It has also been found that there is an excitation cross-section change of a factor ～5 for a corresponding projectile charge state change from 6⁺ to 12⁺, that efforts to classifyK x-ray satellite spectra byLshell vacancy labels (KL ⁰,KL ¹,...) are probably inaccurate due to extensive population ofn≧3 spectator levels, that both the recoil ion and beam-foil spectra exhibit few lines withn≧4, and that for the allowed transitions studied here, collisional excited states quenching effects due to the ～100mTorr target gas pressures used are negligible.     

Femtosecond spectroscopic studies of the one- and two-photon excited-state dynamics of 2,2,17,17-tetramethyloctadeca-5,9,13-trien-3,7,11,15-tetrayne: a trimeric oligodiacetylene

The excited-state dynamics of an oligomer of polydiacetylene, 2,2,17,17-tetramethyloctadeca-5,9,13-trien-3,7,11,15-tetrayne, dissolved in n-hexane have been studied by femtosecond fluorescence upconversion and polarized transient absorption experiments under one- and two-photon excitation conditions. Spectroscopically monitoring the population relaxation in the excited states in real time results in a distinct time separation of the dynamics. It has been concluded that the observed dynamics can be fully accounted for on the basis of the two lower excited states of the target molecule. The S1 (2(1)Ag) state, which cannot be excited from the ground state with one-photon absorption, is verified to be populated via internal conversion in 200+/-40 fs from the strong dipole-allowed S2 (1(1)Bu) state. The population in the "hot" S1 state subsequently cools with a time constant of 6+/-1 ps and decays back to the ground state with a lifetime of 790+/-12 ps.     

Ethers as ligands. Part V(1). Metal(II)-diglyme and -pentaglyme solvates

Summary Eighteen new coordination compounds are reported with diglyme (dgm) and pentaglyme (pgm) as ligands:viz. [M(dgm)₂](SbCl₆)₂ with M=Mg^II, Ca^II, Sr^II, Mn^II, Fe^II, Co^II, Ni^II, Cu^II, and Zn^II; [M(pgm)](SbCl₆)₂ with M=Mn^II, Fe^II,Co^II, Ni^II, Cu^II, and Zn^II; and [M(pgm)](SbCl₆)₂ · H₂O with M=Mg^II, Ca^II, and Sr^II. The metal(II) ions are hexacoordinated by the ether-oxygens of two diglyme molecules or of one pentaglyme molecule. The coordinated diglyme molecules are in the TGTT¯GT conformation.     

Critique of the paper “on the gas-liquid phase transition”

The proof of a recently enunciated theorem on the occurrence of a gas-liquid phase transition is shown to be defective in several respects. Also, it is argued that the theorem itself very probably does not hold.The paper, On the Gas-Liquid Phase Transition by A. C. Biswas appeared inJournal of Statistical Physics 7:131 (1973).