ION HIGH RESOLUTION FOURIER TRANSFORM DIFFERENTIAL SPECTROSCOPY.

Abstract

The easy recognition of the ionic nature of spectrally observed molecules has proven to be very useful after the development of the velocity modulation laser technique by Gudeman and $Saykally^{a}$. Extension of the same method to wideband FT spectra has already been $tried^{b}$, and very successfully applied to plasma diagnostics by Hong and $Miller^{c}$. To our knowledge, no other results are actually published using Doppler modulation Fourier transform spectroscopy. This is the main motivation of the present work. We describe the first attempt to get simultaneously the selective and non selective high resolution FT spectra. The principle is similar to the low resolution vibrational circular dichroism double modulation approach by Nafie and $Vidrine^{d}$. A 1.25 kHz ac voltage is applied to the emitting discharge tube and detected on two channels in quadrature, while the inferferometer path difference is modulated at 0.25 kHz. Tests are performed on the $\Delta v = 1$ sequence vibration-rotation bands of $ArH^{+}$ in the $2500 cm^{-1}$ region.