Peter Gürtler

Spectroscopic investigation of the electronic structure of the chlorine molecule in the VUV

Abstract Vacuum ultraviolet absorption spectroscopy and fluorescence analysis under selective optical excitation have been combined to deduce the electronic structure of Cl2. Between 73000 and 81000 cm−1 five bound electronic states could be analysed. Some of them are affected by pronounced Rydberg—valence mixing. Especially the 1 1∑u+ state clearly yields a double-well structure which results from an avoided crossing between an ionic valence and a Rydberg state. The double-well structure is responsible for an irregular vibrational sequence between 73000 and 74500 cm−1 which either prevented an analysis in earlier investigations or lead to wrong assignments. The FC factors of the 1 1∑u+ fluorescence with its bound—bound and bound—free contributions between ≈ 73000 and 50000 cm−1 are also severely affected by the double-well structure. The results are compared with the first ab initio calculations of the electronic structure of Cl2. In general, excellent agreement is found.

Superlumi: A high flux VUV spectroscopic device for luminescence measurement☆

Abstract A new experimental set up for time and spectrally resolved luminescence experiments on atoms, molecules and solids under state selective excitation with synchrotron radiation (SR) is described. A uniquely large spectral range of luminescence analysis from 50 to 1000 nm is covered by a combination of two monochromators. The central device is a specially designed VUV toroidal grating monochromator with an extremely large ƒ- number 1:28 for a working range from 50 to 300 nm. Excellent agreement between calculated and measured performance of this instrument is found.

Vacuum ultraviolet spectroscopy of the Cl2 molecule trapped in pure neon, pure argon, or mixed neon–argon matrices

Synchrotron radiation excitation and emission spectra with lifetime measurements are reported for the first time in the VUV region for systems consisting of Cl2 molecules trapped in a neon matrix, an argon matrix, and mixed Ar/Ne matrices. In pure neon, the emission spectrum of the D’→A’ ‘‘laser’’ transition at 4.7 eV of the Cl2 molecule is vibrationally well resolved and constitutes an interesting example of UV spectroscopy of a matrix ‘‘isolated’’ molecule. In pure argon or mixed Ar/Ne matrices, new broad emissions at 4.1, 3.8, and 3.5 eV are clearly identified, which result from the specific interaction between Cl*2 and Ar and are attributed to different charge–transfer states of the ArCl+Cl− entity. The Ar concentration dependence and the time‐gated spectra are shown to be especially useful in interpreting the large differences observed between the pure neon and the pure argon matrix case.

Molecular rydberg transitions in carbon monoxide: term value/ionization energy correlation of BF, CO and N2

Abstract The linear correlation between the term value and ionization energy for molecular Rydberg transitions is tested for the sequence of isoelectronic molecules BF, CO and N 2 based on a new measurement of the absorption spectrum of CO and data for BF and N 2 . For the n pσ series and n pπ series converging on the first ionization potential, we find an excellent linear behavior (within 10 meV) corroborating (i) the correlation and (ii) the individual assignments. For Rydberg series leading to the A 2 Π and B 2 Σ + states, where no data for BF are available, a comparison of term values for CO and N 2 is presented.

The experimental station SUPERLUMI: A unique setup for time- and spectrally resolved luminescence under state selective excitation with synchrotron radiation

Abstract An experimental set-up for time- and spectrally resolved luminescence experiments on atoms, molecules and solids under state selective excitation with synchrotron radiation is described. The setup covers a large spectral range from 50 to 1000 nm with three monochromators. A resolution better than 0.1 nm can be obtained for excitation and spectral analysis. The time scale in time-resolved measurements ranges from 50 ps to a few ms.

Luminescence spectroscopy of atomic zinc in rare-gas solids. I

Steady-state and time-resolved luminescence spectroscopy of atomic zinc isolated in thin film samples of the solid rare gases, prepared by the cocondensation of zinc vapor with argon, krypton, and xenon has been recorded at 6.3 K using synchrotron radiation. Pairs of emission bands result from photoexcitation of the singlet 4p 1P1←4s 1S0 resonance transition of atomic zinc, even in annealed samples. In Zn/Ar the pair of emission bands were observed in the uv at 218.9 and 238 nm and for Zn/Xe in the near-uv at 356 and 399 nm. For the Zn/Kr system two emission bands were observed in the uv region at 239.5 and 259 nm but in addition, a weaker band was present in the near-uv at 315.6 nm. In a given annealed rare-gas host, the excitation profiles recorded for all the emission bands are identical, exhibiting the threefold splitting characteristic of Jahn-Teller coupling in the triply degenerate excited 1P1 state. These excitation profiles are identified as the solid phase equivalent of the 4p 1P1←4s 1S0 resonance transition of atomic zinc occurring at 213.9 nm in the gas phase. Based on their spectral positions and temporal decay characteristics, the emission bands observed in the uv and near-uv spectral regions have been assigned as the singlet and triplet transitions, respectively, of atomic zinc. The origin of the pairs of emission bands is ascribed to the Jahn-Teller coupling between noncubic vibronic modes of the lattice and the excited 4p orbital of the 1P1 state of atomic zinc, resulting in the coexistence of two energy minima. In Zn/Ar, the effects of slow vibrational relaxation in the excited singlet state were evident in the relative intensities and temporal decay profiles of the pair of emission bands. Specifically, the lower energy emission band was favored with excitation of the highest energy component of the threefold split Jahn-Teller absorption band, while the higher-energy emission was favored with excitation of the lowest-energy component. The intensity of the triplet state emission was observed to be enhanced in the heavier rare gases, being completely absent in Ar, weak in Kr, and the only emission observed in Xe.

Temperature dependence of the exciton—phonon coupling in the strong coupling limit: Results for solid nitrogen

Abstract High resolution (Δ E = 0.75 meV) absorption profiles of the vibronic bands in the range of the w 1 Δ u ← X 1 Σ + g and a 1 II g ← X 1 Σ + g exciton progressions at hv ≈ 8.9 eV in solid N 2 have been measured in the temperature range between 6 K and 30 K. These excitations are strongly localized so that the observed temperature dependence of the fine structure, consisting of a zero phonon line and a phonon side band, can be described very well in the model of strong exciton—phonon coupling at point defects. The experimental results for the w 1 Δ u transition are found to be consistent with the assumption of a Debye spectrum for the phonon density of states and we derive a value for the Debye temperature of θ = 78 K, which is in very good agreement with that derived from other measurements.

Luminescence spectroscopy of atomic zinc in solid rare gases. II. Temperature dependence

The temperature dependence of the pairs of emission bands present for atomic zinc isolated in annealed solid argon, krypton, and xenon samples is examined in steady-state and time-resolved luminescence spectroscopy. The pairs of emission bands in all the Zn/RG systems exhibited a reversible temperature dependence whereby the intensity of the high-energy band decreased, while the low-energy band gained in intensity with increasing temperature. In the Zn/Ar system, the decrease in the intensity of the 218.9 nm emission band observed between 9 and 28 K was coupled with a concomitant increase in the intensity of the band at 238 nm. In this temperature range the decay times of the 218.9 nm band decreased while the 238 nm band exhibited a constant decay time of 1.41 ns and a rise time correlated with the decay of the 218.9 nm band. The interdependence exhibited by the intensities and decay times of the two emission bands is modeled by an activated nonradiative process with a barrier height of 130.6 cm−1 for pop...

Excimer formation of chlorine in rare gas solids studied by luminescence spectroscopy

Abstract Excitation- and emission spectra of Cl 2 in Neon-matrix, Argon-matrix and Ne-Ar mixtures were measured using synchrotron radiation as excitation source. In Neon, only the laser-emission of Cl 2 at about 4.7 eV was observed. In Argon-matrix as well as in mixtures of Ne and Ar, new emission bands appear, which could be attributed to Cl 2 -Ar complexes. By photolysing the sample, Cl-atoms have been produced, which were stable in the matrix. After photolysis, fluorescence of ArCl and Ar 2 Cl excimers could be observed. By varying the Ar amount in the mixtures, we were able to obtain information about the number of Ar atoms involved in the several complexes.

Self-trapping of excitons in rare gas solids

Abstract From time- and spectrally resolved photoluminescence, self-trapping rates o excitons (Xe, Kr) and the influence of dimensionality on the self-trapping process (Ar) were deduced. The rate of vibrational relaxation of self-trapped states was determined from hot luminescence (Ne).