PUBLICATION ABSTRACTS, W. van Wijngaarden           2002

Lifetimes and Polarizabilities of Low Lying S, P and D States [PDF]

R. Ashby and W. A. van Wijngaarden

Journal of Quantitative Spectroscopy and Radiative Transfer, 76, 467 - 473 (2002)

The radiative lifetimes, scalar and tensor polarizabilities of low lying S, P and D states of lithium are obtained using a Coulomb approximation.  The calculated lifetimes agree very well with the handful of experimental values listed in the literature.  The ground state polarizability is also close to the measured result.  This method requires substantially less computational time than ab initio theory, thereby permitting the study of nearly 40 states.

Axial Molecular Beam Diode Laser Spectrometer for Environmental Monitoring and the Study of Weakly Bound Complexes [PDF]

H. D. Osthoff, W. Jäger, J. Walls and W. A. van Wijngaarden

Proc. SPIE, 4817, 249-257 (2002)

A novel molecular beam spectrometer for the purpose of trace gas sensing is described.  Sensitivity is greatly enhanced and absorption interference by atmospheric H₂O and CO₂ is greatly reduced by using a molecular expansion.  The expansion results in rotational cooling and population enhancement of low-lying energy levels.  The instrument employs a tunable mid-infrared lead salt diode, which operate in single mode from 2348.5 to 2351.1 cm^-1, and a 36 m Herriott multipass cell.  The sample gas is injected axially through a coupling hole in one of the spherical mirrors.  The result is an increase of the residence time of the molecular beam in the sampling region.  Pulsed operation of the nozzle allows background subtracted spectra to be acquired.  The spectrometer can either by operated in fast scan mode, in which the laser frequency is rapidly scanned over the absorption feature of interest, or in frequency modulation mode with 2f-detection.  A special adaptation of frequency modulation to the axial sampling system is described.  Sample data of CO₂ are presented.