ROTATIONAL SPECTRA OF THE H2O-HCCCCH AND HCCCCH-NH3 COMPLEXES

$^{1}$ K. I. Peterson and W. Klemperer, J. Chem. Phys. 81, 3842 (1984). $^{2}$ G. T. Fraser, K. R. Leopold, and W. Klemperer, J. Chem. Phys. 80, 1423 (1984).Author Institution: Seinan Gakuin University; Molecular Physics Division, National Institute of Standards and TechnologyA 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 $C_{2v}$ species. Transitions from $J = 4-3$ to $J = 11-10$ were observed for $K+{a} = 0$ and 1 states of the $H_{2}O$ and $D_{2}O$ species. For the HDO isotopic form only the $K_{a} = 0$ state was detected due to cooling of the higher $K_{a}$ 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 $H_{2}O-HCCCCH$. For the $HCCCCH-NH_{3}$ complex a symmetric-top a-type spectrum was observed for the $^{14}NH_{3} {^{15}}NH_{3}$ and $ND_{3}$ isotopic species of the complex. Rotational analysis of $HCCCCH {^{14}}NH_{3}$ yielded $B = 1067.8309(1) MHz, Dj = 0.3678(8) kHz$ and $D_{3K}= 132.94 kHz$. The $^{14}N$ nuclear electric quadrupole structure was resolved for the lowest frequency transitions of $HCCCCH-{^{14}}NH_{3}$ providing $eQq_{a} = -3.198(5)$ MHz. The molecular electric dipole moment was determined for $HCCCCH-{^{15}} NH_{3}$ to be $\mu = 2.3188(13) D$. The derived molecular structures will be described and comparisons with the closely related complexes $H_{2}O-HCCH_{1}$ and $HCCH-NH_{3} 2$ will be made