A new application for cavity ring-down spectroscopic (CRDS) technique using a pulsed polarized light source has been developed in the absorption measurement of liquids for “colorless” organic compounds using both a single sample cell and double sample cells inserted in an optical cavity at Brewster angle. At present an experimental capability of measuring absorption coefficients as small as 2–5×10−7 cm−1 has been demonstrated by measurement of the absorption baselines. The first spectra for CRDS in the liquid phase, the C–H stretching fifth vibrational overtones of benzene in the pure liquid and hexane solution are obtained. The optical absorption length for liquids in both a single sample cell and double sample cells of 1 cm length is up to 900 cm due to multipass of light within an optical cavity. Compared to the thermal lens and optoacoustic spectroscopic techniques, the sensitivity for CRDS mainly depends on the optical absorption path of the sample (single passing path of the sample times multipass times), is not determined by the laser power and the length of the sample cell. The absolute absorption coefficient and band intensity for the sample are determined directly by the spectroscopy.
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Br ( P j 2 ) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromideThe photodissociation dynamics of diiodomethane molecules has been investigated in the wavelength range of 277-305 nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping, where the ions were generated from ͑2ϩ1͒ multiphoton ionization of I( 2 P 3/2 ) and I*( 2 P 1/2 ) fragments with the same laser as that to dissociate the parent molecules. The speed and angular distributions of I* and I fragments were determined from the images. The translational energy distribution of I*( 2 P 1/2 ) fragment consists of a single Gaussian component ͑named G*͒, while that of I( 2 P 3/2 ) consists of two Gaussian components ͑named G1 and G2͒. It was found that the component G* and G2 show similar angular distributions and similar fragmentation energy partitioning ratios, indicating that these two components originate from dissociation at the same electronically excited state, while the component G1 is from another state. Three fragmentation pathways were employed to account for the experimental observations, the adiabatic dissociation from the 1B 1 state to form I( 2 P 3/2 ) with component G1, the adiabatic dissociation from the 2B 1 state to form I*( 2 P 1/2 ) with component G*, and the nonadiabatic dissociation from the 2B 1 state caused by coupling with the higher 2A 1 state to form I( 2 P 3/2 ) with component G2.
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