W. M. van Herpen

Rotationally resolved laser spectroscopy of tetracene and its van der Waals complexes with inert gas atoms

By using a molecular beam apparatus in combination with a single frequency dye laser we were able to resolve several rovibronic bands in the S1 electronic state of tetracene (C18H12) and its van der Waals complexes with inert gas atoms. The spectra of tetracene have been assigned and rotational constants were derived for the S0 and S1 electronic state. The existence of perturbations in the rotational spectra of the van der Waals complexes is demonstrated.

The trans-stilbene-Ar van der Waals complex. Vibrationally averaged substitution structure in its S0 and S1 electronic states

Abstract Argon atom substitution coordinates, accurate to ±0.02 A, in the S 0 and S 1 states of the trans-stilbene-Ar van der Waals complex have been determined by comparing the inertial constants obtained from fits of two bands in the rotationally resolved electronic spectrum of the complex with those obtained from fits of the corresponding spectrum of the bare molecule (Champagne et al., J. Phys. Chem. 94 (1990) 6). The argon atom is found to be localized above (or below) the plane of one of the aromatic rings by ∼ 3 A in both electronic states but is displaced off the ring center by more than ∼ 1 A in both transverse directions. This geometry is not the one predicted by simple atom-atom pair potentials. Model calculations suggest that this is a consequence of the vibrational averaging that occurs on the S 0 and S 1 surfaces, and that these surfaces are significantly influenced bythe anisotropy of the v

HIGH RESOLUTION ABSORPTION SPECTRUM OF THE MOLECULAR EIGENSTATES OF PYRAZINE

A method is demonstrated to measure high resolution absorption spectra, in the near ultraviolet region, with a bolometer in a molecular beam. The high resolution absorption spectrum of the P, Q, and R branches of the 1B3u (0–0) electronic transition of pyrazine was recorded. The observed residual Doppler linewidth is reduced to 50 MHz in the near ultraviolet region. Simultaneously with the absorption spectrum, the laser induced fluorescence spectrum was observed. A comparison is made between excitation and absorption intensities of the molecular eigenstate spectrum. It is concluded that substantial differences exist between both spectra. The intensities are not proportional, which is most clearly visible in the Q branch. This confirms earlier time resolved measurements and low resolution absorption spectra. However, the quantum yield of various, closely spaced molecular eigenstates is in the same order of magnitude. This observation justifies the approximation of absorption intensities by excitation inten...

ROTATIONALLY RESOLVED SPECTROSCOPY OF DEUTERATED FLUORENE AND THE FLUORENE-ARGON VAN DER WAALS COMPLEX

Abstract With a single frequency tunable UV source in combination with a collimated molecular beam, rovibronic fluorescence spectra were obtained for fully deuterated fluorene and its van der Waals complex with argon. The O 0 0 vibronic band in both molecules was assigned and molecular constants derived. The argon atom in the complex lies above the middle ring of the fluorene molecule. It is shown that substantial zero-point motions are present in the complex, hindering a precise determination of the effective structure.

Hyperfine structure and Λ doubling in the A 2Δ state of CH: Observation of an internal hyperfine perturbation

We report the observation of a resonance between hyperfine states, due to the crossing of rotational ladders at N=10 of Δ5/2 and Δ3/2 spin‐doublet states in the excited A 2Δ state of CH. Accurate values for the hyperfine constants a, b, and c in the A 2Δ state were obtained. From measurements of the Λ‐doublet splittings we estimate an upper limit to the Λ doubling in the A 2Δ state.

High resolution laser spectroscopy as a tool to investigate dynamics in large molecules and molecular clusters

Abstract Much information on the dynamical and structural properties of electronically excited states can be substracted from (ultra) high resolution laser spectroscopy with MHz resolution. This is demonstrated on the radiationless transitions from the first excited singlet state in pyrazine and the spectra of tetracene and its van der Waals complexes with noble gases. In both systems the existence of interstate coupling is clearly observable, while in pyrazine the individual molecular eigenstates have been studied in the frequency and in the time domain.

Rotationally Resolved Spectroscopy of Tetracene and its Van Der Waals Complexes With Inert Gas Atoms

Rovibronic spectra of tetracene (C18H12) and its Van der Waals complexes with argon and krypton have been resolved by using a well collimated molecular beam in combination with a single frequency dye laser. The rotational constants of tetracene have been deduced in the S0 and S1 electronic state. The rovibronic spectra of the Van der Waals complexes show an enhanced intersystem crossing.

The Zeeman spectrum of the OH 2Π12 state

The J = 12 and J = 32 states of the X 2Π12 level of OH have been studied in magnetic fields up to 0.8 T. The molecular beam electric resonance method was used. The Λ-doubling Zeeman transitions have been observed for the J = 12 singular level for the first time. The results were combined with data from the literature, which enabled a rather uncorrelated fit of all the g-factors with improved accuracies. The experimental value of the electronic spin g-factor is compared with the theoretical prediction.

Spectroscopy in the Visible and Near Ultraviolet Region of Some Organic Molecules and their Van Der Waals Complexes

By using a molecular beam apparatus with a single frequency dye laser we were able to resolve several rovibronic transitions of some large molecules and their Van der Waals complexes with noble gas atoms. The rotational constants of tetracene, fluorene and the fluorene- argon complex have been determined. The structure of the complex was derived. In the rotational spectra of the tetracene-noble gas complexes perturbations were shown to be present, increasing with the size and number of the attached atoms. Fluorescence excitation spectra of trans- stilbene and the stilbene-argon complex are reported.