D. Bebelaar

Time resolved molecular spectroscopy using high power solid state lasers in pulse transmission mode. A re-examination of the Sn← S1 spectra of naphthalene and anthracene

Abstract A nanosecond laser spectrometer consisting of a 3nsec ruby/Nd PTM laser, fast detection system and high brightness analysing source is described. An analysis of the geometry considerations is given for crossed beam and collinear arrangement. The excited-state absorption spectra of naphthalene in 3MP at 85°K and 293°K from 14000 to 30000 cm −1 are given. The results provide a direct method to evaluate the quantum yields for fluorescence φ f and intersystem crossing φ T . Also the excited-state absorption spectra of anthracene in PMM from 16000 to 26000 cm −1 and in 3MP from 26000 to 36000 cm −1 are reported.

Time response of various types of photomultipliers and its wavelength dependence in time‐correlated single‐photon counting with an ultimate resolution of 47 ps FWHM

The time response of the classical photomultipliers 56DUVP and XP2020 in time‐correlated single‐photon counting has been measured at several wavelengths between 257 and 630 nm with a best result of 235 ps FWHM. Also, the time response has been measured of the microchannel‐plate photomultiplier R1564U‐01 and the crossed‐field photomultiplier VPM‐154M at the two wavelengths 273 and 546 nm. The best result was 47 ps at λ=273 nm. The use of a fast constant‐fraction discriminator was crucial. The origin of after pulses in the time response curve of photomultipliers is discussed.

MOLECULAR LUMINESCENCE OF SOME ISOALLOXAZINES IN APOLAR SOLVENTS AT VARIOUS TEMPERATURES

Abstract— –Spectral properties of isoalloxazines in organic solvents of low polarity are determined at 300 and 77 K. Vibrational structure in the spectra reveals a vibrational mode of 1250cm‐. The pure electronic transition energies are established to a greater accuracy than was done previously and comparison to theoretical data is made. Actual lifetimes up to 10 ns for fluorescence and 300 ms for phosphorescence are found. The ratio of the actual fluorescence lifetime and the radiative lifetime is found to agree well with the quantum yield. Solvent interactions hardly shift the energy of the first electronically excited singlet state but merely affect the Franck‐Condon envelope of the spectrum and the non radiative decay of the chromophore. In albne solutions at 77 K isoalloxazine clusters are formed exhibiting P‐type delayed fluorescence.

Time resolved mode‐to‐mode vibrational energy flow in the isolated s‐tetrazine argon complex

This paper reports the first direct observation of intramolecular vibrational redistribution (IVR) where two consecutive steps have been distinguished. The initially excited vibronic state ∼(6b2) of the van der Waals complex of s‐tetrazine and argon changes into the intermediate state ∼(16a116b1) from which subsequently the final state ∼(16a2) originates. The temporal intensity profiles of selectively detected emission from each of these states of the complex have been measured on a picosecond time scale.

Excited singlet state polarization and absorption spectra of 1,2-benzcoronene, 1,12-benzperylene and 1,2:3,4-dibenzanthracene

Abstract The direction of polarization and the oscillator strengths of the S n ← S 1 absorption spectra of 1,2-benzcoronene, 1,12-benzperylene and 1,2:3,4-dibenzanthracene in the region 15 000–25 000 cm −1 are reported.

The Lowest Excited Singlet States of 1-Azaadamantane and 1-Azabicyclo[2.2.2]octane: Fluorescence Excitation Spectroscopy and Density Functional Calculations

The lowest excited singlet states of the structurally rigid amines 1-azaadamantane and 1-azabicyclo[2.2.2]octane have been investigated by using fluorescence excitation spectroscopy on samples seeded in supersonic expansions. Based upon the notion that in both species the lowest excited singlet state is a Rydberg state with the ground state of the radical cation as its ionic core, excitation spectra have been analyzed by employing density functional calculations of the equilibrium geometries and force fields of the ground state of the neutral species and its radical cation. A good agreement is obtained between experimentally observed and theoretically predicted frequencies and intensities of vibronic transitions. Subsequent refinements of the geometry of the lowest excited singlet state are shown to account adequately for the minor differences between experiment and the computational results obtained by using the radical cation as a model for the lowest excited singlet state. From our analysis it also bec...

Holder for fast photodiodes in TO‐18 package

The design of a holder for fast photodiodes is described. These holders have been tested with commercially available photodiodes in a standard TO-18 package using delta light pulses from a synchronously pumped cw dye laser. Results of the measurements are presented and the holder is shown to perform well even for an experimental photodiode with a rise time of less than 40 ps and a FWHM of 80 ps.

Photochemical vapor deposition of titaniumdiboride

Abstract Titaniumdiboride (TiB2) is an attractive candidate for wear- and corrosion-resistant coatings. The photothermal deposition of TiB2 by hydrogen reduction of TiCl4 and BCl3 has been studied. In contrast to thermal chemical vapor deposition (CVD), the laser-induced chemical vapor deposition (LCVD) results in a surface reaction rate limited process. High deposition growth rates are obtained and powder production is prevented. The enhancement of the growth rate by UV light from an ArF excimer laser is larger than 40%.

Raman echo on a picosecond timescale in nitrogen gas

Abstract A Raman echo on a picosecond timescale on the υ = 0 → 1 vibrational transition in nitrogen gas (8 atm. ≈ 300 K) was observed. We have used two synchronously pumped dye lasers which were amplified in dye amplifiers. Using the ps pulses from these two dye lasers and the second harmonic from a Nd:YAG laser in a four wave mixing experiment the Raman susceptibility decay (analogous to the free induction decay) and the echo decay were measured.

Conformational dynamics of charge-transfer states in donor- bridge-acceptor systems.

Donor−acceptor compounds containing a phenylenediamine electron donor and a naphthalene, a cyanobenzene, or a cyanonaphthalene acceptor were studied. The two chromophores are connected by three different bridging units, consisting of CH2 groups linked to a semiflexible piperidine or piperazine ring or to a rigid 2,5-diazabicyclo[2.2.1]heptane group. All donor−acceptor compounds show photoinduced charge separation, resulting in the formation of a compact charge-transfer (CCT) state in nonpolar solvents. The conformational change needed to arrive at this species is imposs-