OBSERVATION OF THE j=2j=2, ∣K∣=1|K|=1 LEVELS OF Ar−NH3Ar-NH_{3} BY FAR INFRARED DIFFERENCE FREQUENCY - SIDEBAND SPECTROSCOPY

Author Institution: Department of Chemistry, University of MinnesotaThe states of the weakly bound complex Ar-NH3 correlating to j=2, $|K|=1$ $NH_{3}$ have been observed using a $CO_{2}$ laser difference frequency - microwave sideband spectrometer. Over 150 transitions have been recorded in the vicinity of 48 $cm^{ -1}$. Definitive assignment of several subbands originating in both $\Sigma$ and $\pi$ states of the j=1, $|K|=1$ complex, and terminating in the upper $\pi$ component of the $j=2$, $|K|=1$ complex have been made using combination differences. Assignment of additional subbands are in progress. The spectra are discussed in relation to previous work on this system."

MICROWAVE SPECTRUM AND STRUCTURE OF HF–BF3BF_{3}

Author Institution: Department of Chemistry, University of MinnesotaA new pulsed-nozzle Fourier transform microwave spectrometer has been used to study the complex $HF-BF_{3}$. A symmetric top spectrum is observed with $B=3327.3361(24) MHz, D_{J}=0.01097(36) MHz, D_{JK}=0.0504(10)$ MHz, and $eqQ_{aa} = 2.7833(53)$ MHz for the $^{11}B$ species, and $B=3334.9078(12)$ MHz, $D_{J}=0.01117(12)$ MHz, $D_{JK} = 0.05183(39)$, and $eqQ_{aa} = 5.765(11)$ for the $^{10} B$ species. The data are consistent with a fluorine-bonded structure with and unexpectedly short intermolecular B-F bond length of 2.51 {\AA}. {Ab initio} calculations, which greatly facilitate location of the spectrum, further predict an approximately $2^{\circ}$ out-of-plane distortion of the $BF_{3}$ in the complex, and a B-F-H bond angle of $108^{\circ}$. This latter result suggests that the complex is a symmetric top due to only to rapid vibrational averaging of the HF orientation. The short bond length and the small but non-zero distortion of the $BF_{3}$ are indicative of an incipient donor-acceptor interaction, which is somewhat surprising for fluorine