Using　the　ab　initio　method,　the　vibrational　and　electronic　spectra　of　binuclear　molybdenum　clusters　which　contain　Mo2OnS4-n(n　=　0-4)　core　were　investigated.　The　main　absorption　bands　in　the　IR　spectra　of　these　clusters　are　assigned　and　compared　with　each　other,　especially　for　the　case　of　the　trans　isomers.　The　electronic　spectra　were　studied　by　performing　the　CIS　calculations.　The　ground　state　and　the　first　excited　state　of　the　clusters　were　discussed　by　using　the　natural　bond　orbital　method.　It　is　shown　that　the　band　corresponding　to　the　longest　wavelength　can　be　assigned　to　three　kinds　of　transition　types.　Two　transitions,　sigma(Mo-Mo)　--＞　pi*(Mo-X-t)(X　=　S,O)　and　sigma(Mo-Mo)　--＞　sigma*(Mo-Mo),　can　be　seen　in　most　cases.　(C)　1999　Elsevier　Science　B.V.　All　rights　reserved.