Sol-gel clad fiber-optic waveguides are investigated as intrinsic distributed fiber-optic chemical sensors. The porous sol-gel cladding allows diffusion of analytes into the evanescent field region close to the fiber-optic core. Pulsed optical excitation (0.5 ns) and time-resolved emission detection can be used to simultaneously monitor several multiplexed sensor clad regions along a single optical fiber. Time-resolved detection is also demonstrated as a means of resolving both the spatial location and the fluorescence kinetics of intrinsic sensor chromophores along the fiber-optic waveguide. Narrow band excitation and spectrally resolved emission provide additional experimental means for discriminating between specific sensor clad regions. A fluorescein-doped silica xerogel clad pH sensor and an undoped aluminosilica xerogel clad quinone sensor are demonstrated as intrinsic sol-gel clad fiber-optic sensors.Fiber-optic chemical sensors provide an efficient and inexpensive method for selective, in situ, real-time chemical sensing. [1][2][3][4] The active sensor region of a fiber can be either immobilized at the distal end of an optical fiber (extrinsic) 2,5 or distributed along the length of the fiber-optic waveguide (intrinsic). 6,7 Submicrometer sized extensive fiber-optic sensors have also been reported, 8

The first vibrational spectrum of the 1-methylallyl radical is detected using resonance Raman spectroscopy with excitation from 237 to 232 nm. The vibrational frequencies of five symmetric fundamentals, the H 3 C-CCC bend, the CCC bend, the H 3 C-C stretch, the C-H in plane bend, and the CH 2 scissors, of the 1-methylallyl radical are reported. The even overtones of the CH 3 torsion, the C-H out of plane bend, the H 3 C-CCC bend, and the CCC bend are identified. The vibrational assignments of the resonance Raman spectra are based upon comparison with calculated vibrational frequencies generated by UHF method using a 6-31G* basis set and experimental values for the allyl radical, the β-methylallyl radical, and similar molecules. Excitation at 236.05 and 234.95 nm yields significant resonance enhancement of overtone and combination bands associated with the H 3 C-CCC bend and CCC bend, respectively. The variation of intensities in the Raman spectra with excitation wavelength yields excited state vibrational frequencies for the H 3 C-CCC bend and CCC symmetric bend of 305 and 502 cm -1 , respectively. Examination of the observed intensity patterns in the resonance Raman spectra indicates that the initial excited state dynamics of the 1-methylallyl radical are dominated by bending motions of the carbon chain.