15min:

HANS NAUS AND WIM UBACHS, Vrije Universiteit, Department of Physics and Astronomy,
De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.

Cavity RingDown Spectroscopy (CRDS) has been used to investigate the b^{1 +}_g~-~X^{3 -}_g system of oxygen isotopomers. The absorption bands of this system are very weak due to the strongly forbidden character of gerade-gerade and ⁺- ^- transitions, and they can only be observed via a magnetic dipole transition moment. The four allowed branches are a factor of 10⁹ weaker than typical electric dipole allowed transitions. The high sensitivity (10^-9~cm^-1), obtained even in a short cell (< 1 m), makes CRDS ideal for spectroscopy on isotopically enriched samples.

Our studies yield updated or new values for the molecular constants of the b^{1 +}_g~-~X^{3 -}_g (v', 0) bands for v'= 0-3 of oxygen isotopomers. These values may help to identify emission bands from excited vibrational levels of O₂ (b^{1 +}_g), including minority isotopomers, as observed in the Earth's atmosphere and can aid in the interpretation of weak signals in the search for possible violation of the symmetrization postulate in ¹⁶O₂.