RECENT MICROWAVE STUDIES OF FREE RADICALS AND OTHER UNSTABLE SPECIES.

Author Institution: Atomic Physics Division, National Bureau of Standards, Infrared and Microwave Spectroscopy Section Washington, D. C., 2023

THE MICROWAVE SPECTRUM OF BH3PF3BH_{3}PF_{3}.

Author Institution: National Bureau of StandardsTransitions in the ground vibrational state for $B^{11}H_{3}PF_{3}, B^{10}H_{3}PF_{3}, B^{11}D_{3}PF_{3}, B^{10}D_{3}PF_{3}$, and $B^{11}D_{2}HPF_{3}$, have been assigned and a structure determined. The parameters are: $d(BH) = 1.207 \pm 0.003$ {\AA}, $d(PF) = 1.538 \pm 0.004$ {\AA}, $d(PB) = 1.836 \pm 0.006$ {\AA}, $\angle HBH = 115^{\circ}04' \pm 32'$ and $\angle FPF = 99^{\circ}50' \pm 26'$. For $B^{11}H_{3}PF_{3}, B^{11}D_{3}PF_{3}$, transitions have also been observed for the low frequency vibrational states. These transitions follow a normal symmetric rotor pattern for $B^{11}D_{3}PF_{3}$, and $B^{11}H_{3}PF_{3}$, however, a strong perturbation occurs between the two lowest vibrations. This gives rise to an unusual pattern. The barrier to internal rotation has been tentatively estimated to be 3 Kcal/mole

DIRECT MICROWAVE MEASUREMENTS OF TRANSITIONS BETWEEN l-TYPE RESONANCE DOUBLETS IN HCN AND DCN.

Author Institution: National Bureau of Standards, Infrared \& Microwave Spectroscopy SectionThe $\Delta$ vibrational levels $(2 \nu^{2}_{2}$) of HCN and DCN are split by a rotational resonance with the nearby $\Sigma$ vibrational level $(2 \nu^{0}_{2}$). At high J values the splitting becomes large enough so that $\Delta J = 0$ transitions between $\Delta$ levels can be observed at microwave frequencies. Transitions for $J = 15$ to $J = 23$ have been observed in HCN and DCN. The agreement with calculated values will be discussed. New measurements on the usual l-doublet transitions will also be presented

MICROWAVE STUDIES OF SHORT-LIVED FREE RADICALS

Author Institution: National Bureau of Standares; Catholic UniversityAn apparatus with several novel features has been constructed for the study of microwave spectra of short-lived free reaicals. The radicals are produced by chemical reaction at the entrance to the waveguide cell and pumped rapidly through it. The spectrum of the SO radical has been completely analyzed and molecular constants determined. Lines from other transient species have been observed, but their identification has not yet been confirmed

MICROWAVE STUDIES OF SOME (CH3)3CH_{3})_{3} AB MOLECULES

Author Institution: National Bureau of Standards“A number of molecules of the type ($CH_{3})_{3}AB$ have been investigated in the microwave region. In those cases where the internal rotation of the $CH_{3}$ groups is strongly hindered, the spectra are found to follow symmetric-rotor patterns. These patterns have been analyzed in detail for ($CH_{3})_{3}N, (CH_{3})_{3}P, (CH_{3})_{3}CH$, and $(CH_{3})_{3}CF$. Rotational transitions in a number of exeited vibrational states, including those associated with the $CH_{3}$ torsional modes, have been identified, and the vibrational frequencies have been determined from relative intensity measurements. The torsional frequencies have been used to derive information on the potential function for internal rotation. In these four molecules the potential terms which involve coupling among the three $CH_{3}$ groups are found to be relatively small. The effects of I-type doubling in degenerate vibrational states of these molecules have also been analyzed. Molecular structures have been determined with the aid of $C^{14}$ isotopie species, and electric dipole moments have been measured from the Stark effects. The trends in these molecular parameters will be discussed.

INFRARED-MICROWAVE DOUBLE RESONANCE USING A CO2CO_{2} LASER.

Author Institution: National Bureau of StandardsExperiments in which a vibrational transition is saturated with a laser source and the microwave rotational spectrum used to monitor the effect are described. In these experiments the pumped and monitored transitions may or may not share a common level. Many molecular systems have been investigated but to date positive effects have been obtained only with $CH_{3}Br$. A decrease in the intensity of certain microwave transitions of methyl bromide was observed when the gas sample was exposed to the laser irradiation; this effect is completely reversible and the time constant is essentially that associated with the microwave detection system (approximately 0.1 second). The results will be discussed with respect to the definite selection rules for collisional transfer of rotational energy

LOW-FREQUENCY INFRARED SPECTRA OF BUTADIENE AND SOME DERIVATIVES

Author Institution: Molecular Spectroscopy Section, National Bureau of StandardsThe infrared spectra of 1,3 butadiene and several derivatives (including fluoroprene, isoprene, and chloroprene) have been investigated in the $250-600 cm^{-1}$ region in an effort to establish the low-frequency skeletal modes. The lowest in-plane fundamental in butadiene itself has been located at $303 cm^{-1}$; the analogous fundamental in the derivatives falls between 250 and $290 cm^{-1}$. The C-C single bond torsional fundamental in fluoroprene is found to be $156 cm^{-1}$ from the microwave spectrum, and probably has a similar frequency in the other compounds. The correlation of the other skeletal bending modes will be discussed. The $A_{u}$ fundamental of butadiene at $525 cm^{-1}$ shows well-resolved rotational structure which confirms the planar trans conformations of the molecule

HCN TRANSITIONS RESPONSIBLE FOR LASER ACTION IN THE SO-CALLED CN LASER.

Author Institution: National Bureau of StandardsThe four laser lines near 337 microns which have been observed in the so-called CN laser have been explained as due to ${\Delta}J = - 1$ transitions involving the $11^{1}0$ and $04^{\circ}0$ vibrational levels of HCN. The laser action seems to arise from a large population inversion which favors vibrational levels involving C-N stretching vibrations. Transitions between the $11^{1}0$ and $04^{\circ}0$ levels are observed because of the mixing of the two levels due to a Coriolis interaction. The 129 micron lines are similarly explained as due to transitions between the $12^{\circ}0$ and $05^{1e}0$ and the $12^{2d}$ and $05^{1d}0$ levels. The 211 micron lines probably arise from the $13^{1}0$ and $06^{2}0$ levels