Normal coordinates calculation and valence force field for propyne, propargyl halides, butyne-2, halobutyne-2, and 1,4-dihalobutyne-2

Force constants and normal modes were evaluated using an overlay technique for CH3CCH, CH3CCD, CD3CCH, CD3CCD, CH2FCCH, CH2ClCCH, CH2BrCCH CH3CCCH3, CH3CCCH2Cl, CH3CCCH2Br, CH2FCCCH2F, CH2ClCCCH2Cl and CH2BrCCCH2Br. Particular attention has been given to diagonal and off-diagonal force constants related to linear bending coordinates. The force field reported in this paper gives such a satisfactory frequency fit that it should provide a good starting point for the explanation of the peculiar band widths of 1,4-dihalobutyne-2.