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The microwave spectra of nine isotopic species of borane monoammoniate (11BH3NH3, 10BH3NH3, 11BH3ND3, 10BH3ND3, 11BD3NH3, 11BH3 15NH3, 10BH3 15NH3, 11BD2HNH3, 11BH3ND2H) have been observed. The rotational constants, centrifugal distortion constants, dipole moment, torsional barrier, and molecular geometry of borane monoammoniate were determined from these spectra. The rs structure is: BN=1.6576(16) Å, BH=1.2160(17) Å, NH=1.0140(20) Å, ∠NBH=104.69(11), ∠BNH=110.28(14). The dipole moment is 5.216(17) D. The torsional barrier about the B–N bond, V3, is 2.047(9) kcal mol−1 for 11BH3ND2H and 2.008(4) kcal mol−1 for 11BD2HNH3.

Harmony et. al. a recently published some design specifications for a smaller version of a FTMW spectrometer. In this work they used a perpendicular nozzle arrangement and found that even though the size of the vacuum chamber and Fabry-Perot cavity mirrors had been greatly reduced, the overall sensitivity was nearly the same as a conventional sized resonator. In an effort to establish FTMW spectroscopy as a viable new technique for analytical chemists, we have constructed a spectrometer of similar size for use as an analytical instrument. The vacuum chamber of the instrument is based on a multi-port 12" sphere. An integral end-flange mirror permits a coaxial nozzle arrangement which greatly improves the sensitivity. The movable cavity mirror rides on a fast motorized stage which allows tuning to any frequency within the range of the spectrometer in 1-2 sec. The entire ! spectrometer is mounted on a mob ile cart for transporting to other laboratories. The per-pulse sensitivity of this smaller instrument is about a factor of 2-3 less than a conventional sized instrument, however the smaller vacuum chamber allows the nozzle to be pulsed much faster without overloading the vacuum pumps. These two factors offset so that the ultimate sensitivity (given one to two minutes of averaging) is approximately the same.

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The microwave spectra of the formamide–water and formamide–methanol complexes have been investigated with a pulsed beam Fabry–Perot cavity Fourier transform microwave spectrometer. The observed hyperfine structure due to the 14N nuclear quadrupole interaction was used to assign the rotational transitions for both species. For formamide–water the rotational analysis of ten transitions provides the constants: A=11 227.931(1) MHz, B=4586.9628(10) MHz, C=3258.8278(7) MHz, eQqaa =1.332(3) MHz, and eQqbb =2.037(3) MHz. The formamide–methanol spectrum exhibits an additional splitting from internal rotation of the methyl group. Eighteen observed transitions from the A and E symmetry states have been assigned and fitted with the rotational constants: A=10 186.594(6) MHz, B=2090.36(59) MHz, and C=1762.80(56) MHz with hyperfine constants close to those of formamide–water. By assuming a methyl top moment of inertia Iα =3.206 uÅ2, the barrier to internal rotation V3=231.01(17) cm−1 is obtained. This barrier height is about 36% smaller than that of methanol. The structures determined for these complexes agree well with prior ab initio calculations which indicate essentially planar, double hydrogen bonded structures for both species.