ROTATIONAL SPECTRA AND STRUCTURE OF THE FULMINIC ACID-ACETYLENE VAN DER WAALS COMPLEX

Pulsed-beam Fourier-transform microwave spectroscopy was used to observe the rotational spectra of $HCNO-C_{2}H_{2}$ and H$CNO-C_{2}HD$. A partial analysis of the $^{14}N$ nuclear electric quadrupole hyperfine structure of the normal isotopic species was carried out yielding values of $eQqa=0.167(5)$ MHz, $eQqb=293(4)$ MHz and $eQqc=-0.126(5)$ MHz. Fits of the a- and b-type transitions of the normal isotopic species to a quartic Watson Hamiltonian give the following rotational constants (in MHz): $A=10257.324(34)$, $B=2122.284(9)$ and $C=1748.446(7)$. Dipole moment measurements of the normal isotopic species find $\\mu_a=0.513(6) D $and $\\mu_b =3.156(4) D$. The structure is planer with inertial defects for $HCNO-C_{2}H_{2}$ and $HCNO-C_{2}HD$ of 1.6448 and 1.6190 $\\mu$ \\AA$^{2}$, respectively. Assuming fixed monomer geometries, the distance between the centers of mass of fulminic acid and acetylene is calculated to be 3.77 {\\AA} from the moments of inertia. Two structural forms are consistent with the spectroscopic data. For both of these forms the molecular axes of fulminic acid and acetylene are approximately between perpendicular ($T$ shaped) and parallel orientations. One form appears to be hydrogen-bonded with an acetylenic hydrogen-oxygen distance of 2.41 {\\AA}. Consideration of H-H van der Waals distances in the second form indicate that the hydrogen-bonded structure is likely the observed form.