Photoelectron (PE) spectra of two stable carbenes 7 and 8 have been recorded and the spectra have been interpreted with the aid of eigenvalues and eigenvectors taken from Becke3LYP calculations. For the carbene series 6-8, the lone pair on the carbene carbon atom is the HOMO. The first adiabatic ionization potential (IP) of eight electronically quite different carbenes has been calculated using semiempirical PM3 and ab initio HF, Becke3LYP, and Becke3PW91 methods (3-21G(*) and 6-31+G* basis sets) as well as the CBS-4 model. For the first vertical IP, the HAM/3, Becke3LYP, and Becke3PW91 methods have been employed. CBS-4 and DFT calculations show excellent agreement with experimental values. Considering both accuracy and speed, the method of choice for the prediction of first ionization potentials of carbenes seems to be Becke3LYP/6-31+G*//Becke3LYP/3-21G(*).Key words: carbenes, electronic structure, first ionization potential, photoelectron spectroscopy, quantum chemical calculations.
