Thermal lens technique: a new method of absorption spectroscopy.

Both a single beam and a dual beam (with synchronous detection) thermal lens technique have been employed in the measurement of "colorless" organic compounds in the range 15,700 to 17,400 cm-1. Combination overtones of C-H stretching vibrations in benzene have been identified and agree with previous results obtained by conventional spectroscopy with a long optical path. Extinction coefficients as low as 1 X 10(-6) liter mole-1 cm-1 have been accurately determined. The sensitivity of the technique has been further demonstrated by measuring the So leads to T1 absorption of anthracene; the spectrum compares favorably with results obtained by conventional techniques.