Transmission FTIR Spectroscopy

Transmission FTIR spectroscopy is a powerful tool being used to investigate the interaction of gases and solid surfaces. In the Grassian group laboratory this tool is used to probe the reactions of different atmospheric gases with environmental interfaces including mineral dust particles such as oxides, carbonates, clays and zeolites. Custom made infrared cells used in these studies are specially designed such that both surface and gas phase measurements can be made simply by moving the infrared cell within the internal compartment. The cell is a stainless steel cube with two BaF2 windows and sample holder jaws. These cells are attached to gas handling systems composed of gas manifolds, pressure gauges and vacuum system. There is also a solar simulator that can be directed onto the infrared cell for studies of photochemical reactions.

Two different types of IR cells are currently being used in our laboratory. One is a stainless steel cell with heating and cooling capabilities This cell is used to study the chemical/photochemical reactions of mineral dust particles with noncorrosive atmospheric gases such as carbon dioxide, oxygen and water vapor. The sample holder (left) that consists of a 3 cm × 2 cm tungsten grid held in place by nickel jaws. The nickel jaws are attached to copper leads so that the sample can be resistively heated. A thermocouple wire attached directly to the tungsten grid is used to measure the temperature of the sample. The sample can be either pressed or coated onto half of the tungsten grid. Heating system allows cleaning the sample surfaces to get rid of water or any other impurities as well as to carry out temperature controlled reactions at 100-900 K. Furthermore, a sample holder with a stainless steel coolant system with copper power leads welded to the end of a stainless steel pipe can be used for the cooling experiments. This sample holder is connected to the reaction chamber using copper gasket and screws.

The other IR cell contains sample holder jaws entirely coated with Teflon. It is especially used to study the chemical/photochemical reactions of corrosive atmospheric gases such as nitric acid and hydrochloric acid. Acid resistant Teflon coating minimizes possible interfering wall reactions of acids with stainless steel. Gas handling system of the Teflon coated cell is completely made from glass and Teflon tubing.