Rotational spectrum of the v11Â =Â 1 and v14Â =Â 1 vibrational states of CH3CCCCH

The pure rotational spectra of the v11 = 1 and v14 = 1 vibrational states of the main isotopic species of methyldiacetylene have been recorded and assigned in the 80-400 GHz frequency range, spanning the quantum numbers 19 ⩽ J ⩽ 95 and 0 ⩽ K ⩽ 15. The present study allows us to provide accurate rotational, centrifugal distortion and vibration-rotation interaction constants. The experimental investigation has been strongly supported by quantum-chemical computations at the second-order Møller-Plesset theory (MP2) in conjunction with a triple-zeta quality basis set.