Johannes Heinze

A Study of the Singlet-Triplet Perturbations in the a 1au State of Acetylene by High-Resolution Ultraviolet Spectroscopy

Laser‐induced fluorescence spectra of the 330 K10 and 340 K10 vibronic bands of the A 1Au←X 1Σ+g transition in acetylene have been recorded with a resolution of 18 MHz. Each rotational transition consists of a group of lines due to coupling of the electronically excited singlet state with isoenergetic triplet states. Using the standard deconvolution procedure the singlet–triplet coupling elements and the density of coupled triplet states are derived for rotational levels up to J=4 in both bands. From the density of coupled triplet states it is concluded that the A 1Au state is perturbed by the T1 3B2 state. Magnetic field measurements have shown that the predissociation of acetylene in the 4ν3’ vibrational level of the A state is caused by a coupling via the T1 3B2 state with predissociating vibrational levels of the electronic ground state.

Acetone, a laser-induced fluorescence study with rotational resolution at 320 nm

The forbidden S1 <-- S0 transition of acetone has been investigated by laser-induced fluorescence measurements with a resolution of 270 MHz. The rotational structure demonstrates, that (i) one deals with a-type transitions and (ii) there is a strong coupling between the torsional motion of the two CH3 groups and the tunneling, out-of-plane wagging motion (nu(23)) of acetone. The interpretation of torsion-vibrational combination bands is less conclusive and thus the discussion still has a preliminary character.

High resolution electronic spectroscopy on the OH-Ar van der Waals complex

Abstract In this study, we report high-resolution measurements of the electronic transition OH (A 2 Σ + , υ′ = 0)-Ar ( 1 S), υ′ = 4 and 5←OH (X 2 Π, υ″ = ))-Ar( 1 S), υ″ = 0 using pulsed dye amplification of cw laser radiation. Rotational line splittings were observed which are attributed to hyperfine structure in the excited state. Accurate values have been determined for the rotational constants in the ground and excited states.

The B 1Πu potential energy curve and dissociation energy of 39K2

The 39K2 B 1Πu potential energy curve has been determined using laser spectroscopic techniques and quantum mechanical calculations. The dissociation energy is 2407.6±0.5 cm−1 (0.2985±0.0001 eV) including a potential barrier of 298±10 cm−1 (0.037±0.0013 eV) found with its maximum at 8.08±0.05 A (15.3±0.1 bohr). The long‐range behavior matches smoothly onto the form predicted from dispersion forces. The dissociation energy of the ground state X 1Σ+g, obtained by a long‐range extrapolation of the vibrational separations, is De =4444±10 cm−1 (0.5506±0.0013 eV), in agreement with recent theoretical prediction.

Quasibound levels and shape resonances of 39K2(B 1Πu) crossed laser‐molecular beam studies and analytical interpretation

Quasibound levels and shape resonances in the (B 1Πu −X 1Σ+g) band system of 39K2 have been recorded by crossed laser‐molecular beam techniques. Using optical–optical double resonance, individual rovibrational levels (v‘=15–18, J‘=3–25) of the K2 state are prepared by Franck–Condon pumping (FCP) in a supersonic nozzle beam. Excitation into quasibound levels below and above the (B 1Πu) state barrier is detected as molecular and atomic (K4 2P3/2→4 2S1/2 only) fluorescence. The resonance transition frequencies and shapes are measured and the results are used (a) to determine the scattering resonance energies, widths, and lifetimes; (b) to compare them with values obtained by a ‘‘maximum internal amplitude’’ approach [R. J. LeRoy and R. B. Bernstein, J. Chem. Phys. 54, 5114 (1971)]; and (c) to check the agreement with exact calculations of the B state potential using the ‘‘inverted perturbation approach (IPA).’’ The bound and quasibound part of the B 1Πu state including the locus (R=8.08±0.05 A) of the barrie...

Collisional processes in the O2B3Σu− state

Abstract Collisional processes, which influence quantitative laser-induced fluorescence (LIF) measurements involving the B 3 Σ u − state of molecular oxygen, were investigated. Since the B state is strongly predissociating, these processes are though to be important only at higher pressure. However, we found that in LIF experiments in methane/air flames in the pressure range between atmospheric pressure and 40 bar collisional quenching and rotational energy transfer (RET) are important even at moderate pressures. Total quenching cross sections of 30(± 10) A 2 for ν′ = 2 and 100(± 30) A 2 for ν = 0 and total RET cross sections of 40(± 16) A 2 were found. An upper limit of 0.7 A2 for the cross section for vibrational energy transfer (VET) out of ν′ = 2 could be determined.

Rotational assignments in the S1 (1B3u) state of pyrazine by UV – UV pump-probe laser spectroscopy

Abstract We have applied an UV—UV pump-probe experiment to the O 0 0 S 1 ( 1 B 3u ← S 0 ( 1 A g ) vibronic transition in pyrazine. The use of two single-frequency lasers and a molecular-beam apparatus made it possible to verify experimentally the rotational assignments for the strongest lines in the high-resolution spectrum of the S 1 state in pyrazine. The experimental results confirm the previously made identifications.

High-resolution spectroscopy on the a-similar-1b1(0, 6, 0) - x-similar-1a1(0, 0, 0) transition in sicl2

Abstract High-resolution laser-induced fluorescence spectra of Si 35 Cl 2 and Si 35 Cl 37 Cl have been observed in a molecular beam. A spectral resolution of 8 MHz was obtained on the A 1 B 1 (0, 6, 0) ← X 1 A 1 (0, 0, 0) transition around 323 nm, which allowed the dense rotational structure of this electronic transition to be completely resolved. The rotational constants in the A 1 B 1 (0, 6, 0) state reflect the almost 22° opening of the ClSiCl bond angle on going from X to A , whereas the SiCl bond length decreases slightly.