LASER SPECTROSCOPY OF THE MOLECULAR-IONS OR THE CHEMISTRY BETWEEN EARTH AND SKY

Experimental techniques of high-resolution infrared spectroscopy are d escribed with an emphasis to the chemistry in the plasma of electrical gas discharges. The spectroscopy of molecular ions has been one of th e most dynamic fields in molecular spectroscopy since the detection of the H-3+ ion by T. Oka in 1980. Almost all recent observations of ion s in the gaseous phase have been achieved by using tunable infrared so urces such as colour-centre lasers, diode lasers and difference-freque ncy laser systems. The progress was also supported by the introduction of velocity modulation for spectroscopic investigations of ions by Gu deman and Saykally. Without these techniques, progress would have been much slower, because the concentration of ionic species in the gaseou s phase is very small and, therefore, the observed lines we very weak. Furthermore, the weak lines of molecular ions are often buried under the much more intense lines of neutral gases which are used to form th e ions in a discharge.