Knowledge Bank

The ground state torsion-rotation spectrum of the asymmetric internal hydroxyl rotation in propargyl alcohol ($HCCCH2OH$) has been investigated in the 84 to 640 GHz range. The ground state has been confirmed to consists of two torsional sub-states of the gauche $conformera$, a symmetric gauche state ($gauche+$) and an antisymmetric gauche state ($gauche-$). No evidence of a low lying third state or trans conformer has been observed. The more stable gauche + state is 652389.5 MHz below the gauche- state. Due to their close proximity, the two gauche states interact strongly through a series of $a$- and $b$-type corilolis interactions. Strong $a$- and weak $b$-dipole rotational transitions are observed within each sub-state while strong $c$-dipole rotational transitions are observed between the two sub-states. Over 2300 transitions covering a range of J and $Ka$ values to 80 and 34, respectively, have been fit to experimental accuracy using a fixed-frame-axis method (FFAM) Hamiltonian. The rotation, distortion and interaction constants have been determined. The 652 GHz gauche + gauche- energy difference, strong $gauche+$ to gauche- transitions and the constants derived from the analysis should enable rapid astronomical detection.