A combined cavity ringdown （CRD） and laser induced fluorescence （LIF） spectroscopic study on the A1∑＋-X1∑＋ transition of Cull has been presented. The Cull molecule, as well as its deuterated isotopologue CuD, are produced in a supersonic jet expansion by discharging H2 （or D2） and Ar gas mixtures using two copper needles. Different profiles of relative line intensities are observed between the measured LIF and CRD spectra, providing an experimental evidence for the predissociation behavior in the A1∑＋ state of Cull. The lifetimes of individual upper rotational levels are measured by LIF, in which the J＇-dependent predisso- ciation rates are obtained. Based on the previous theoretical calculations, a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A1∑＋ state and the lowest-lying triplet 3∑＋ state, and a tunneling effect may also be involved in the predis- sociation. Similar experiments are also performed for CuD, showing that the A1∑＋ state of CuD does not undergo a predissociation process.
Transitions of the 6υ3 overtone band of ^14N2 ^16O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10^-4 cm^-1 allowed us to reveal finer ro-vibrational couplings taking place after J〉14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6υ3 band obtained in this work and those from previous studies is given.
Moisture measurement is of great needs in semiconductor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy （CRDS）. By using different absorption lines of H20 in the 1.56 and 1.36 gm regions, we are able to determine the relative concentration （mole fraction） of water vapor from a few percent down to the 10-12 level. The quantitative accuracy is examined by comparing the CRDS hygrometer with a commercial chilled-mirror dew-point meter. The high sensitivity of the CRDS instrument allows a water detection limit of 8 pptv.
