Microwave Spectra Of A Potential Four-fold Internal Rotor, Phenylsulfur Pentafluoride

We present the microwave spectra of the fourth molecule containing the four-fold rotor -SF$_{5}$, phenylsulfur pentafluoride, c-C$_{6}$H$_{5}$-SF$_{4}$-F (PhSPF). The first three molecules in this series were vinylsulfur pentafluoride (VSPF), propen-1-ylsulfur pentafluoride (PSPF) and buten-1-ylsulfur pentafluoride (BSPF). VSPF exhibited splitting into the A, E, and B torsional states with 10's of MHz between the torsional transitions. PSPF exhibited the torsional splitting with 10's of kHz between transitions. BSPF exhibited no torsional splitting. Likewise, PhSPF shows no torsional splitting in the spectra. This phenomenon is mostly explained by the differences in the values of the four-fold barrier to internal rotation, V$_{4}$, in this series of molecules

Gamma-Ray Polarimetry of Two X-Class Solar Flares

We have performed the first polarimetry of solar flare emission at gamma-ray energies (0.2-1 MeV). These observations were performed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for two large flares: the GOES X4.8-class solar flare of 2002 July 23, and the X17-class flare of 2003 October 28. We have marginal polarization detections in both flares, at levels of 21% +/- 9% and -11% +/- 5% respectively. These measurements significantly constrain the levels and directions of solar flare gamma-ray polarization, and begin to probe the underlying electron distributions.Comment: 33 pages, 12 figures, accepted for publication in Ap

AN INVESTIGATION OF THE NUCLEAR QUADRUPOLE COUPLING TENSORS OF 2-BROMOPYRIDINE USING THE EXTENDED TOWNES-DAILEY ANALYSIS

The rotational spectrum of 2-bromopyridine was measured with a cavity FTMW spectrometer, and the complete nuclear quadrupole coupling tensors of $^{79}$Br, $^{81}$Br, and $^{14}$N were determined. These tensors are interpreted using the Extended Townes-Dailey (ETD) analysis\footnote{S.~E.~Novick \textit{J.~Mol.~Spectrosc.} \underline{\textbf{267}}~13-18,~2011.}. which allows us to predict orbital electron populations. These results are compared to \textit{ab initio} Intrinsic Atomic Orbital (IAO) populations. The ETD analysis for the $^{14}$N nucleus requires expressing the orbitals as \textit{sp}$^{2}$ hybrids and performing rotations on the measured quadrupole tensors and the calculated IAO populations

THE SCIENCE AND HUMANITY OF WILLIAM KLEMPERER, THE MIDDLE AND LATER YEARS

William Klemperer and his research group, using Molecular Beam Electric Resonance (MBER) spectroscopy, studied a plethora of weakly bound complexes until and beyond his retirement from teaching at Harvard at age seventy-five in 2002. Many of Klemperer’s research students and postdoctoral associates went on to prolific careers of their own. Bill’s last public seminar was presented in 2013 and his last publication on weakly bound complexes appeared in 2015 at age eighty-eight

TORSIONAL SPLITTING AND FOUR-FOLD BARRIER TO INTERNAL ROTATION: THE ROTATIONAL SPECTRA OF VINYLSULFUR PENTAFLUORIDE

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.4]{vpfs.eps} \end{wrapfigure}The rotational spectra of vinylsulfur pentafluoride, and three isotopologues (S-34 and both C-13's) have been recorded in the frequency region of 6 GHz to 20 GHz. Measurements were made using both cavity and chirped pulse Fourier transform microwave spectrometers. The four-fold barrier to the internal rotation of the –SF$_5$ group against the vinyl group has been approximated from the spectral data which is possible due to the observation of easily resolved pure rotational transitions in each of the $A$, $B$, and doubly degenerate $E$ torsional substates. All transitions were successfully fit simultaneously using the ERHAM code. We note that this work, we believe, represents the first use of pure rotational spectroscopy to characterize a four-fold barrier internal rotation problem. Rotational constants, structure, and the internal rotation barrier height will be presented and compared to results from quantum chemical calculations

Microwave Spectra and ab Initio Studies of Ar-Propane and Ne-Propane Complexes: Structure and Dynamics

Microwave spectra in the 7-26 MHz region have been measured for the van der Waals complexes, Ar-C H3 C H2 C H3, Ar- C13 H3 C H2 C H3, Ne20 -C H3 C H2 C H3, and Ne22 -C H3 C H2 C H3. Both a - and c -type transitions are observed for the Ar-propane complex. The c -type transitions are much stronger indicating that the small dipole moment of the propane (0.0848 D) is aligned perpendicular to the van der Waals bond axis. While the 42 transition lines observed for the primary argon complex are well fitted to a semirigid rotor Hamiltonian, the neon complexes exhibit splittings in the rotational transitions which we attribute to an internal rotation of the propane around its a inertial axis. Only c -type transitions are observed for both neon complexes, and these are found to occur between the tunneling states, indicating that internal motion involves an inversion of the dipole moment of the propane. The difference in energy between the two tunneling states within the ground vibrational state is 48.52 MHz for Ne20 -C H3 C H2 C H3 and 42.09 MHz for Ne22 -C H3 C H2 C H3. The Kraitchman substitution coordinates of the complexes show that the rare gas is oriented above the plane of the propane carbons, but shifted away from the methylene carbon, more so in Ne propane than in Ar propane. The distance between the rare gas atom and the center of mass of the propane, Rcm, is 3.823 Ã… for Ar-propane and 3.696 Ã… for Ne-propane. Ab initio calculations are done to map out segments of the intermolecular potential. The global minimum has the rare gas almost directly above the center of mass of the propane, and there are three local minima with the rare gas in the plane of the carbon atoms. Barriers between the minima are also calculated and support the experimental results which suggest that the tunneling path involves a rotation of the propane subunit. The path with the lowest effective barrier is through a C2v symmetric configuration in which the methyl groups are oriented toward the rare gas. Calculating the potential curve for this one-dimensional model and then calculating the energy levels for this potential roughly reproduces the spectral splittings in Ne-propane and explains the lack of splittings in Ar-propane

Internal dynamics in the molecular complex of CF3CN and H2O

The rotational spectrum of trifluoroacetonitrile–water complex has been studied by pulsed-nozzle, Fourier transform microwave spectroscopy. Both a-type and b-type transitions have been observed. The rotational constants, centrifugal distortion constants, and the 14N nuclear quadrupole coupling constants have been determined. The complex is T-shaped, with the oxygen atom from the water located 3.135 Å from the carbon atom of CF3 of the trifluoroacetonitrile molecule

The Covalent Interaction between Dihydrogen and Gold: a Rotational Spectroscopic Study of H₂-AuCl

The pure rotational transitions of H2-AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer equipped with a laser ablation source. The structure was found to be T-shaped, with the H-H bond interacting with the gold atom. Both 35Cl and 37Cl isotopologues have been measured for both ortho and para states of H2. Rotational constants, quartic centrifugal distortion constants, and nuclear quadrupole coupling constants for gold and chlorine have been determined. The use of the nuclear spin-nuclear spin interaction terms Daa, Dbb, and Dcc for H2 were required to fit the ortho state of hydrogen, as well as a nuclear-spin rotation constant Caa. The values of the nuclear quadrupole coupling constant of gold are Xaa=-817.9929(35) MHz, Xbb=504.0(27) MHz, and Xcc=314.0(27). This is large compared to the eQq of AuCl, 9.63 312(13) MHz, which indicates a strong, covalent interaction between gold and dihydrogen