Biomedical subjects

Gerard Meijer

Publications and source records attributed to Gerard Meijer.

5 recordsLinked to original sources

PubMed2003

Infrared spectroscopy of niobium oxide cluster cations in a molecular beam: identifying the cluster structures.

Infrared spectra of niobium oxide cluster cations are measured via IR multiple photon dissociation spectroscopy in the 400-1650 cm(-1) region. The cluster cations are obtained directly from a laser vaporization source and irradiated with the infrared light emitted by a free electron laser. For those oxide clusters that fragment after excitation, the IR spectra are recorded by measuring the cluster intensity changes as a function of the IR wavelength. The spectra of all examined oxide clusters exhibit two main absorption features that can be assigned to vibrations of terminal (Nb=O) or bridging (Nb-O-Nb) oxide groups. For selected clusters DFT calculations at the B3LYP/LACVP* level have been performed and the calculated vibrational spectra are compared to the experimental data to identify the gas phase structures of the clusters.

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PubMed2002

Longitudinal focusing and cooling of a molecular beam.

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.

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PubMed2002

Cold molecules.

During the last years there has been a rapidly growing interest in the field of cold molecules. This has obviously been inspired by the spectacular successes in the closely related field of cold atoms, which have recently been recognized by the award of the 2001 Nobel Prize in Physics to Cornell, Ketterle, and Wieman. But molecules have much more to offer than simply extending the experiments already performed with atoms to more complex species.

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PubMed2002

Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy.

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.

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PubMed2002

Alternate gradient focusing and deceleration of a molecular beam.

Neutral dipolar molecules can be decelerated and trapped using time-varying inhomogeneous electric fields. This has been demonstrated only for molecules in low-field seeking states, but can, in principle, be performed on molecules in high-field seeking states as well. Transverse stability is then much more difficult to obtain, however, since molecules in high-field seeking states always experience a force towards the electrodes. Here we demonstrate that an array of dipole lenses in alternate gradient configuration can be used to maintain transverse stability. A pulsed beam of metastable CO in high-field seeking states is accelerated from 275 to 289 m/s as well as decelerated from 275 to 260 m/s.

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