The construction and application of a new versatile spectroelectrochemical cell is described. The spectroelectrochemical cell is equipped with a specially constructed mirror-type working electrode and operates in the reflection mode. By use of a micrometer, semi-infinite and finite diffusion conditions can be realized. Owing to careful sealing, measurements in highly purified solvents, as well as in more unusual solvents such as liquid SO2, can be carried out. In particular, measurements of NiOEP (OEP=2,3,7,8,12,13,17,18-octaethylporphyrin-dianion) in liquid SO2 show that excellent conversion times of less than is can be achieved under thin-layer conditions. These are the first spectroelectrochemical measurements in liquid SO2 ever described.