The THF/H~2O binary clusters have been studied by the molecular beam, the VUV from synchrotron radiation and the TOF mass spectrometry technique. The (THF)~n(H~2O)~mH^+(n=2～5, m=0～n-1) cluster ions were observed in the mass spectroscopy. It was noticed that the (THF)~n (H~2O)~n~-~2H^+(n=2～5) cluster ions had larger intensity than the others and were regarded as "magic number" ions. By using ab initio MO method at HF/3-21G basis set level, the structures of (THF)~n(H~2O) ~n~-~2H^+(n=2～4) cluster ions have been optimized. The theoretical calculations help to explain the "magic number" appearance in the experiment and are in agreement with the experimental results.

Key words: TETRAHYDROFURAN, AB INITIO CALCULATION, MOLECULAR ORBITAL THEORY, SYNCHRONOUS RADIATION, TIME-OFF FLIGHT MASS SPECTROMETRY