This instrument is designed to study ice surfaces relevant to terrestrial and extra-terrestrial environments. The basic conditions prevailing in outer space are ultrahigh vacuum with a base pressure range <10^-12 torr, and low temperatures, in the range of 5-200 K. The whole instrument is maintained at ultrahigh vacuum with several vacuum pumps connected in series. There is a target substrate of Ru(0001) single crystal (Princeton Scientific Corp.) inside the chamber which can be cooled to a temperature as low as 8 K using a closed cycle helium cryostat connected with a temperature controller and heater. It can maintain any temperature of interest. Thin layers of various molecular solid (ice) surfaces, such as water, alcohols, carbon monoxide etc., can be created by vapor depositing on the precooled single crystal substrate. The reactivity of such a molecular solid surface is probed by various techniques. Low energy ion scattering mass spectrometry is one of those. This technique uses reactive ions produced by electron impact ionization (EI) which are then mass and energy selected by quadrupole mass analyzer and subjected to collide on the desired molecular solid surfaces. The scattered ions from the surfaces are analysed by another quadrupole mass spectrometer. Together with this, we have a temperature-programmed desorption mass spectrometer (TPD-MS) to probe the surface desorbing species, a low-energy alkali-ion gun to trigger out the neutral species present on the surface, and a reflection absorption infra-red spectrometer (RAIRS) for getting the infra-red spectrum of surface species. To study the photochemistry of the ice, this instrument is equipped with a vacuum ultraviolet source (Deuterium lamp with magnesium fluoride window).