J. Bahrdt

Triplet states of CO trapped in rare gas crystals

Vibrational progressions due to the au20093Π, a’u20093Σ+, du20093Δ, and eu20093Σ− states of CO in Ar, Kr, and Xe crystals are observed in absorption. Two groups of phonon sidebands separated from the zero phonon lines by about 4 and 8 meV for the a’u20093Σ+ and du20093Δ states are attributed to librations and to localized phonons. The broad absorption bands, the even broader emission bands, and the large Stoke shift of the au20093Π transition are treated in terms of a configuration coordinate model by a momentum analysis. A quadratic coupling has to be invoked with relaxation energies in the excited states increasing from 14 meV for Ar to 95 meV for Xe and with relaxation energies in the ground state increasing from 29 meV for Ar up to 1278 meV for Xe. The changes of the configuration coordinate of 0.2 to 1.5 A are also discussed with the help of two pair potential models.

Vibrationally hot emission and electronic relaxation of CO in Ne matrix

Vibrational progressions due to radiative decay of Au20091Π (v’=0, 2, 3 5, 6, 8), eu20093∑ (v’=0, 3, 5, 12), a’u20093∑ (v’=5, 14), du20093Δ (v’=3, 5), au20093Π (v’=0, 1, 2) to the ground state and of eu20093∑ (v’=3, 5, 7, 9, 11, 12) and du20093Δ (v’=3, 7, 11) to the au20093Π state have been observed for selective excitation of Au20091Π (v’=0,u2009.u2009.u2009.u2009,8). The intersystem crossing rate constants, the bottle necks, pathways and rate constants for internal conversion in the triplet levels and the triplet–singlet radiative rate constants are explained by an intramolecular mixing of electronic states and electron–phonon coupling with the matrix.

Bottlenecks for radiationless electronic and vibrational relaxation of N2 in solid Kr matrices

Infrared emission due to Wu20093Δu (v’=4)u2009→u2009Au20093Σ+u (v‘=1,u20092) and B’u20093Σ−u (v’=6)u2009→u2009Bu20093Πg (v‘=1,u20092) transitions of N2 molecules isolated in Kr matrices has been observed. The bottlenecks for radiationless relaxation which allow for a competition by these rather slow radiative transitions are identified by selectively populating individual vibrational levels in the vibrational progression of the Au20093Σ+u, Bu20093Πg, au20091Πg, and wu20091Δu states.

A metastable state of CO in Ar matrix at about 11 eV

Abstract A metastable state in the energy range from 10.7 to 11.1 eV with a lifetime of about 15 ms is tentatively assigned to a CO quintet state. It is populated nonradiatively after excitation of a Rydberg state and it decays nonradiatively to a strongly mixed a 3Σ+-b3Σ+ state which is observed in phosphorescence.

Electronic energy transfer between O2 and CO dopants in Ar crystals

Excitation spectra of Ar crystals doubly doped with O2 and CO show the au20093Π, a’u20093∑+, du20093Δ, eu20093∑−, Au20091Π vibrational progressions of CO as well as the Schumann Runge bands (u2009Bu20093∑−u) and the following dissociation continuum of O2. In emission the Cameron bands (au20093Π) of CO and the Herzberg bands Cu20093Δu of O2 have been observed. No electronic energy transfer from CO to O2 or vice versa occurs. This rules out an intramolecular V–E conversion of high vibrational quanta (v=32) in the electronic ground state of CO to the au20093Π (v=3) state of CO and subsequent electronic energy transfer to O2 in the recently reported IR‐induced UV‐visible fluorescence in matrix‐isolated CO thus supporting the other suggested intermolecular V–E and V–V transfer routes.

Electronic and vibrational relaxation of CO in Ar and Kr matrices

Abstract Vibrational progressions due to radiative decay of e 3 Σ(ν′ = 0, 4, 6, 8), a′ 3 Σ(ν′2,6), d 3 Δ(ν′= 4, 6, 8) and a 3 Π(ν′=0) to the ground state or to the a 3 Π state have been observed for CO in Ar and of e 3 Σ(ν′ = 4, 8) and d 3 Δ(ν′ = 4, 8) for CO in Kr by selective excitation of A 1 Π(ν′ = 0, … 8). The bottlenecks, the intersystem crossing and the internal conversion rate constants are explained by an intramolecular mixing of electronic states and electron-phonon coupling with the matrix. For internal conversion in the singlet states an additional matrix-induced nonadiabatic matrix element exceeding 20 cm −1 has to be postulated for Kr. A long-lived Rydberg state is observed for CO/Ar.

Ray tracing of a high flux beamline

Abstract An anamorphotic focussing mirror system between the synchroton radiation source and the entrance slit of a monochromator has been optimized by ray tracing calculations.

Vibrational relaxation and electronic energy transfer of N2 aggregates in solid Xe matrices

Population distributions of vibrational levels within the first excited electronic state A3Σu+ of N2 molecules embedded in a Xe matrix have been derived from emission spectra resulting from selective excitation of individual levels with monochromatized synchrotron radiation. The steady-state population distributions strongly depend on the originally excited level and are incompatible with a simple stepwise nonradiative relaxation process between successive vibrational levels. The experimental distributions are attributed to relaxation by nonradiative electronic energy transfer processes between neighbouring N2 molecules via exchange interaction. The cascade in the A3Σu+ state involves relaxation to lower energies in steps of two vibrational quanta and an up conversion of the energy in steps of three vibrational quanta. The probability of these processes follows an energy gap law for the excess energy.

Vibrationally hot emission and electronic relaxation of Co in Ne matrix

Vibrational progressions due to radiative decay of A1P(v = 0,2,3,5,6,8) e3S(v = 3,5,12), a3S(v = 11,14),d3D(v = 5) to the ground state and of e3S(v = 3,7,9,11,12), d3D(v = 3,7,11) to the a3P state were obsd. for selective excitation of A1P(v = 0, ..., 8). The intersystem crossing rate consts., the bottle necks, pathways and rate consts. for internal conversion in the triplet levels and the triplet-singlet radiative rate consts. are explained by an intramol. mixing of electronic states and electron-phonon coupling with the matrix. [on SciFinder (R)]

Vibrational relaxation of N2 aggregates in rare gas matrices

Abstract Vibrational levels of the A 3 Σ + u state are depopulated by non-radiative electronic energy transfer between N 2 molecules due to exchange interaction. The vibrational quantum number v′ is reduced in steps of Δv′ = 2 and in an additional process it is also increased in steps of Δv′ = 3 in the course of relaxation.