S. Stolte

Laser induced predissociation of SF6 clusters

Abstract Dimer predissociation is sensitively detected as attenuation of the SF + 5 ion signal from a SF 6 molecular beam crossed by a line tunable cw CO 2 laser. The dimer spectra show a double peak structure which is assigned to the symmetric and anti-symmetric combination of the v 3 vibration. The minimum observed linewidth is 3 cm −1 fwhm.

Van der waals modes and rotational fine structure in C2H4 dimers

Abstract IR predissociation spectra for C2H4 dimers have been recorded, using a cw CO2 laser as source of radiation and a Ge bolometer as detector. Apart from the main peak around 952 cm−1, two extra peaks at 916 and 986.3 cm−1 have been observed. Those two peaks are discussed in terms of van der Waals combination modes and, from their relative intensities, dimer temperatures in He-seeded beams have been obtained. Observed peaks show rotational fine structure with a 10 MHz linewidth, which implies a predissociation lifetime of 16 ns.

Raman overtone spectroscopy of ethylene

Abstract For ethylene (C 2 H 4 ) overtone Raman Q-branches have been measured between 800 and 6300 cm −1 . The observed bands amongst which transitions as weak as 10 −4 times the Raman ν 1 intensity are assigned. Anharmonic resonances manifest themselves in enhanced Raman scattering intensities at band origins neighbouring a strong transition, e.g. for 2ν 10 , ν 2 and ν 3 and for 2ν 12 , ν 1 , 2ν 2 and ν 2 + 2ν 10 . For the out-of-plane modes 2ν 3 , 2ν 7 and 2ν 4 this resonance has been found to be much weaker or even absent. Even five triple and one quadruple combination band could be assigned. The band origin of ν 4 + ν 7 = 1964 ± 2 cm −1 (species B 1g ) has been obtained from the Δ K = 2 transitions.

Vibrational overtones of the homonuclear diatomics (N2, O2, D2) observed by the spontaneous Raman effect

Abstract With a powerful 500 W Ar+-laser intracavity arrangement at wavelength 488 nm. spontaneous cw Raman spectra of the fundamental and first overtone vibrations are recorded for the homonuclear diatomic molecules N2, O2 and D2. From the measured Raman intensities values for α″/α′ are extracted and compared, for D2 and N2, to ab initio calculations.

The Raman spectrum of ethane from 600 to 6500 cm−1 stokes shifts

Abstract The vibrational Raman Stokes spectrum of ethan (C2H6) has been recorded from 600 to 6500 cm−1 using the powerful focused radiation of a free running Ar-ion laser. Measurements in bulk and in jet were performed in an intracavity arrangement. The present analysis is concentrated on totally, symmetric transitions. Numerous Q branches of overtones and binary combination tones appeared in the spectrum. All first overtones of both the degenerate and non-degenerate modes have been observed. Several multiple combination tones have also been identified. Some hot bands due to transitions starting from the thermally excited v4 torsional level appeared as satellite Q branches. From the measured band origins the anharmonic shifts are determined and a table with the anharmonicity constants is constructed. The occurrence of a few very strong Fermi resonances enhancing the intensity of otherwise weak bands has been observed. A comparative study of some overtone Raman spectra of three substituted ethanes (CH3 CF3, CH3, CH3 SiH3, CH3 CD3) has been undertaken. The existence of a strong interaction between the CH3 symmetric stretching modes and the overtones of the asymmetric deformation modes appears to be characteristic only for the CH3CH3 and CH3CD3 molecules.

Molecular beams of CF3Br probed by spontaneous raman effect and excited with a CO2 laser

Abstract The state population of CF3Br is found to be entirely non-thermal under certain molecular beam conditions; the various vibrational modes show distributions which can be described using mode-temperatures differing by as much as a factor of 1.7. Considerable vibrational excitation (ν1, ν2 + ν3) was produced with a focused cw CO2 laser. A structured excitation spectrum was observed.

Infrared predissociation of SiF4 and CF3Br clusters in a molecular-beam experiment

Abstract IR predissociation spectra of SiF4 and CF3Br clusters have been studied by attenuating a molecular beam with a line-tunable cw CO2 laser. T

IR dimer spectroscopy and Fermi resonance

Abstract A careful discussion of Fermi resonances is shown to explain qualitatively the many observed line shifts from molecular-beam infrared predissociation experiments.

The allene Raman spectrum from 250 to 6200 cm−1 stokes shift☆

Abstract Using a powerful intracavity and focused beam of a free running Ar-ion laser operating at 488 nm, the Raman Stokes spectrum of allene (C 3 H 4 ) has been recorded from 250 to 6200 cm −1 . Attention is concentrated on the numerous Q branches of overtones and combination tones appearing in the spectrum. All first overtones of both the degenerate and non-degenerate modes have been observed, except for ν 9 and the CH stretching vibrational modes. Moreover, several combination tones are identified. In some cases hot bands have been observed belonging to transitions starting at the thermally excited ν 10 and ν 11 levels. From the measured band origins anharmonic shifts are determined yielding (cross-) anharmonicity constants, sometimes in combination with the vibrational angular momentum coefficients. Similar to the case of C 2 H 4 , Raman combination tone intensities appear sometimes to be enhanced by an anharmonic resonance of the vibrational level with a strong Raman active first excited state. This “Fermi borrowing” of Raman activity tends to be enhanced especially when major amplitudes occur along similar bond features. In most cases the anharmonicity shifts of overtone and combination band origins follow the standard term formula. A (incomplete) table of x ij and g ij values has been constructed. Special spectral features have been observed around the 2ν 10 overtone Q branch. The relative Raman band strength of the ν 1 and 2ν 1 Q branches for similar molecules has been compared quantitatively.

Orientational hole burning for dimers in the limit of large rotational quantum numbers

Abstract Dimers can often be treated as prolate symmetric tops, with their symmetry axis along the dimer axis. In that case, thermal excitation results in J , M J ⪢ K if the moment of inertia around the dimer axis can be assumed much larger than the moment of inertia along an axis perpendicular to it. Expressions are derived which describe the near saturation behaviour of perpendicular and parallel excitations; for J , M J ⪢ K , simple analytical expressions are obtained.