Opto-acoustic

Opto-Acoustic Spectroscopy Applied to the Detection of Gaseous Pollutants... 

POLLUTION DETECTION WITH OPTO-ACOUSTIC SPECTROSCOPY... 

SPIN FLIP RAMAN LASER OPTO-ACOUSTIC SPECTROMETER... 

In the above I have very briefly sketched the opto-acoustic pollution measurement techniques and described a few examples where the technique has been applied to problems of scientific, industrial, and societal significance. It is clear that these techniques are simple and practical and will play increasing by important roles in pollution monitoring. 

Table I shows that in either dioxane or acetonitrile the quantum yield for degradation of I, is unaffected by the presence of 0.1 M of triplet quencher, either sorbic acid, naphthalene or cyclohexadiene. In ethanol, triplet quenchers reduce < >d from 0.34 to 0.14. Quantum yields for intersystem crossing, as determined by a laser opto-acoustic technique ( ), were 0.36 in ethanol and 0.59 in dioxane. These results agree with our earlier report (3), and indicate that significant reactivity occurs from St of I in protic solvents, and that reaction occurs exclusively from Sx in aprotic solvents. While triplet quenching experiments cannot rigorously exclude participation by short-lived higher triplet states, Palm et al (9) have obtained conclusive evidence from CIDNP experiments for singlet-state participation in a series of aryloxy-acetophenones. Note that the triplet state of I is formed in aprotic solvents, and that in deaerated solutions at room temperature it decays by first-order kinetics with a lifetime of 200 ns (3). Remarkably, despite having lifetimes about 100 times longer than other, differently-substituted, aryloxyacetophenones (the longer lifetimes may...

Borsarelli, C.D., Braslavsky, S.E., Sortino, S., Marconi, G., and Monti, S. (2000) Photodecarboxylation of ketoprofen in aqueous solution. A time-resolved laser-induced opto-acoustic study, Photochem. Photobiol., 72, 163-171. 

Vibrational energy relaxation in methyl halides has been investigated using opto-acoustic methods. In one system the phase-lag between the pressure wave and the modulated excitation source was monitored, while in the other pulsed excitation was employed and the transient photoacoustic signal was observed. 

Figure 4. Refractive index n(T) and opto-acoustic dispersion function E)(q °, T) of PVAC (O, ). n(T = 295 K) measured with an AbW refractometer at A, = 514.5 nm.

Figure 5. Refiactive index n ( , ) and opto-acoustic dispersion function D90AR 0 of EPON as a function of temperature T. Solid line refiactive index at A. = 514.5nm ( , measured with an AbW refiactometer) dashed line refiactive index for white light ( measured with an Abb6 refiactometer).

C.K.N. Patel, Use of vibrational energy transfer for excited-state opto-acoustic spectroscopy of molecules. Phys. Rev. Lett. 40, 535 (1978)... 

A.M. Angus, E.E. Maiinero, M.J. Colles, Opto-acoustic spectroscopy with a visible CW dye laser. Opt. Commun. 14, 223 (1975)... 

Measurement of the photo- (or opto-) acoustic signal following the partial nonradiative dissipation of laser radiation absorbed by one or more compounds in a gaseous or liquid medium. Detection of ultralow concentrations of impurities. Used also in combination with gas and liquid chromatographies... 

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