The Microwave Spectrum and Molecular Constants of Trifluoromethyl Acetylene

Abstract

Pure rotational transitions, $J=4\ensuremath{\rightarrow}5,6\ensuremath{\rightarrow}7, \mathrm{and} 8\ensuremath{\rightarrow}9$ have been measured for C${\mathrm{F}}_{3}$CCH and $J=5\ensuremath{\rightarrow}6 \mathrm{and} 8\ensuremath{\rightarrow}9$ for C${\mathrm{F}}_{3}$CCD. These yield for C${\mathrm{F}}_{3}$CCH, ${B}_{0}=2,877.948$ Mc/sec, ${D}_{J}={0.2}_{4}$ kc/sec, ${D}_{\mathrm{JK}}=6.3$ kc/sec, and for C${\mathrm{F}}_{3}$CCD, ${B}_{0}=2,696.073$ Mc/sec, ${D}_{J}={0.2}_{6}$ kc/sec, ${D}_{\mathrm{JK}}=6.2$ kc/sec. If $\ensuremath{\angle}\mathrm{FCF}$ is tetrahedral, $d(C\ensuremath{\equiv}C)$ and $d(\mathrm{CH})$ are assumed to be 1.207A and 1.056A, respectively, then the bond lengths $d(\mathrm{CF})=1.330\mathrm{A}$ and $d(\mathrm{C}\ensuremath{-}\mathrm{C})=1.493\mathrm{A}$ are obtained. Rotational frequencies of molecules in excited bending vibration modes have been measured and found to agree with Nielsen's theory of $l$-type doubling.