Knowledge Bank

A pulsed-beam Fabry-Perot cavity Fourier transform microwave spectrometer has been employed in the measurement of the rotational spectra of the hydrogen-bonded complexes of diacetylene with water and ammonia. The molecular beam was produced from Ar seeded with about 1% of diacetylene and 1% of either water or ammonia. For the H2O-HCCCCH species an a-type spectrum was observed which was characteristic of a plansr prolate $C2v$ species. Transitions from $J=4-3$ to $J=11-10$ were observed for $K+a=0$ and 1 states of the $H2O$ and $D2O$ species. For the HDO isotopic form only the $Ka=0$ state was detected due to cooling of the higher $Ka$ states in the supersonic expansion. Spectral analysis provided the molecular constants $B=1065.4515(2)$ MHz and $C=1062.0299(2)$ MHz and a dipole moment $\mu a=2.2971(12)D$ for $H2O-HCCCCH$. For the $HCCCCH-NH3$ complex a symmetric-top a-type spectrum was observed for the $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}NH3\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}NH3$ and $ND3$ isotopic species of the complex. Rotational analysis of $HCCCCH\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}NH3$ yielded $B=1067.8309(1)MHz,Dj=0.3678(8)kHz$ and $D3K=132.94kHz$. The $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$ nuclear electric quadrupole structure was resolved for the lowest frequency transitions of $HCCCCH-\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}NH3$ providing $eQqa=-3.198(5)$ MHz. The molecular electric dipole moment was determined for $HCCCCH-\mathrm{<mrow\; data-mjx-texclass="ORD">15</mrow>}NH3$ to be $\mu =2.3188(13)D$. The derived molecular structures will be described and comparisons with the closely related complexes $H2O-HCCH1$ and $HCCH-NH32$ will be made.