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Step-Scan Fourier Transform Vibrational Circular Dichroism Measurements in the Vibrational Region above 2000 cm-1
Volume 51, Number 4 (April 1997) Page 508-511
Long, Fujin; Freedman, Teresa B.; Tague, Thomas J.; Nafie, Laurence A.
We present the results of a new Fourier transform infrared vibrational circular dichroism (FT-IR-VCD) spectrometer optimized for performance in the near-infrared region above 2000 cm-1. The instrument is capable of operating in either the conventional rapidscan mode or the step-scan mode and is designed around the Bruker IFS 55 FT-IR spectrometer. We find that in the region of hydrogen stretching, the instrument performs as well as or better than (depending on the spectral coverage and resolution desired) a corresponding dispersive grating VCD spectrometer, with noise levels at approximately 10-6 Delta A units for a two-hour collection at 8-cm -1 resolution. The performance is approximately a factor-of-2 better in signal-to-noise ratio in optimized step-scan operation in comparison to the corresponding results in rapid-scan operation. The reasons are traced to advantages in electronic filtering and undersampling efficiency in step-scan mode. It is expected that the advantages of step-scan will increase with increasing optical transition frequency, such as the region of overtone and combination bands between 4000 and 8000 cm-1.