Removal of I(2)absorption lines from 514-nm excited Raman spectra

The intense excitation of an Ar(+) laser operating at 514 nm enhances the grating ghosts and general stray light within most double monochromators at wavelengths close to the exciting line. The I(2) filter technique provides an effective means of reducing this interference and, in so doing, makes possible the measurement of Raman bands close to the exciting line. However, at an instrument resolution less than 3 cm(-1), the I(2) absorption spectrum seriously interferes with the Raman spectrum. Ratioing the Raman spectrum with a white light absorption spectrum of I(2) removes the I(2) absorption lines. However, with slit widths <3 cm(-1), the wavelength reproducibility of the monochromator on successive scans is not high enough to insure successful ratioing. A technique is described for obtaining, approximately within the same time interval, the Raman spectra and white light spectrum at each wavelength that data are acquired. This procedure accurately removes the I(2) absorption spectrum.