#P HF/6-31G(d) freq=HPModes HF/6-31G(d) freq acetylene 0 1 X1 X2 1 1.0 C3 2 r3 1 90.0 C4 2 r3 1 90.0 3 180.0 H5 2 r5 1 90.0 4 180.0 H6 2 r5 1 90.0 3 180.0 r3=0.592723 r5=1.649676