Knowledge Bank

The microwave spectra of unstable, gaseous fulminic acid $H12C14N16O$ and five more of its isotopic species have been studied in the frequency range from 10 to 46 GHz. The spectrum of molecules in the ground vibrational state established the linearity of the chain HCNO. The following rotational constants $Bu$ for the ground state were obtained: $$\begin{array}{ll} B_{0}(H^{12}C^{14}N^{16}O) = 11 469.04 MHz &B_{0}(D_{12}C^{14}N^{16}O) = 10 292.51 MHz\B_{0}(H_{13}C^{14}N^{16}O) = 11 091.57 MHz &B_{0}(H^{12}C^{14}N_{17}O) = 11 151.69 MHz\B_{0}(H^{12}C^{14}N^{18}O) = 10 865.34 MHz &B_{0}(D^{13}C^{14}N^{16}O) = 10 011.18 MHz. \end{array}$$ From these a combined $ra-$ and $r0-$ structure has been evaluated: $r(C-H)=1.027\pm 0.001\backslash AA,r(C-N)=1.161\pm 0.015\backslash AA,r(N-O)=1.207\pm 0.015$ {\AA}. The rather large uncertainties in the CN- and NO-distances are due to the proximity of the N-atom to the center of gravity. It appears to be the first time that, in the same molecule, two different $l$-type doublets $(\Delta l=0\Delta J=+1)$ and their corresponding series of $l$-type doubling transitions $(\Delta l=2,\Delta J=0)$, arising from the two degenerate bending modes ($v4=1$ and $v5=1$), have been observed. The analysis of the two $l$-type doubling series revealed a marked dependence of the $l$-type doubling constants $q4$ and $q5$ on higher powers of the angular momentum J. Additional rotational transitions of the molecules in excited vibrational states have been observed and will be discussed. The molecular dipole moment was determined from Stark-effect measurements of the $J=0\to 1$ transition in the ground state and found to be $3.06\pm 0.15$ Debye. The nuclear quadrupole coupling constants for the $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$-and $\mathrm{<mrow\; data-mjx-texclass="ORD">17</mrow>}O$-nuclei can be given as $$eqQ(^{17}O)=-12.31 \pm 0.12, MHz, and, |eqQ (^{14}N)| \leqq 0.3 MHz.$$