PES of C4H9+ Structural Isomers and Determination of the Global Minima of XC3H6+ (X =Li to Br) via G3 Calculations

Three levels of theory, B3LYP/6-311+G**, MP2(full)/6-31G* and G3, had been used to elucidate the energetic and structural relationships of XC3H6+ (X = Li to Br) isomers. The B3LYP calculations had been replaced by MP4(SDTQ)/6-31G(d,p)//MP2(full)/6-31G(d) in the determination of the potential energy surfaces, PES, for C4H9+ structural isomers. This had been done to facilitate the comparison with the available published data. The relative stabilities of local minima had been calculated. Enthalpies of formation,, had been also determined via G3 method. Comparison of the calculated values with the available experimental data reveals an excellent correlation between the two sets. The obtained XC3H6+ global minima had been compared with those of XC2H4+ and and the differences had been justified.