Chester O. Britt

Microwave Spectrum, Internal Rotation, Dipole Moment, Quadrupole Coupling, and Structure of Nitrosomethane

The microwave spectra of CH3NO and CD3NO have been observed and analyzed. The barriers to internal rotation are 1137 ± 5 and 1095 ± 7 cal/mole for CH3NO and CD3NO, respectively, a difference of 42 cal/mole which is thought to be real. The barriers were calculated by the internal‐axis method with retention of higher terms in the usual Fourier expansion of the rotational energy and computation of the torsional integrals in the harmonic‐oscillator approximation. The theoretical parameters were fitted to the data by a least‐squares method and the uncertainties reported are standard deviations. Transitions having comparable Stark and quadrupole energies were used to calculate the dipole moment. Secular equations of second or third order were solved for each of the data points. The dipole moment components are μa = 2.240 ± 0.001 D, μb = 0.522 ± 0.006 D, and μtotal = 2.300 ± 0.002 D. The quadrupole coupling constants of CH3NO are 0.50 ± 0.16, −6.016 ± 0.031, and 5.518 ± 0.031 for the components along the a, b, a...

Microwave Spectrum of Nitrosobenzene in Excited Vibrational States

The rotational spectrum of nitrosobenzene in the first four excited states of the torsional vibration has been observed. The vibrational fundamental is at about 100 cm−1. The barrier to rotation around the C–N bond is 3.9±1 kcal/mole, based on relative intensity measurements. Variations in the inertia defect in the excited states are compared with theory. The next‐lowest vibrational state is at about 220 cm−1 and is an in‐plane vibration.

Microwave spectrum of nitrocyclopropane

The microwave spectrum of nitrocyclopropane has been investigated in the 8–40‐GHz region. Transitions in the ground state and five excited states of the torsional mode have been assigned. The ground state of a monodeuterated nitrocyclopropane has also been assigned. The conformation of the molecule is found to be the bisected one with the plane of the nitro group perpendicular to the plane of the cyclopropyl ring. The torsional frequency (70± 20 cm−1) of the nitro group and the barrier to internal rotation (1100± 500 cm−1) have been derived from relative intensity measurements of transitions in the ground and first torsional states. The dipole moment is found to be 3.95± 0.10 D.

Microwave Spectrum, Structure, and Barrier to Internal Rotation of Pentafluoroethane

The rotational spectrum of CF3CHF2 has been studied in the 8.4‐ to 26.5‐Gc/sec region, with c‐type, R‐branch transitions being assigned for both the ground vibrational state and the first excited torsional state. With the assumptions that rC–H=1.10 A, ∠CCH=110°, rF–F=2.162 A for the CF3 group, that the CF3 group is symmetrical and its axis and the C–C bond are collinear, and that the CHF2 fluorines are equivalent, an approximate structure of rC–F=1.335 A, ∠FCF=108.14°, rC–C=1.520 A, rC–F′=1.345 A, ∠F′CF′=109.06°, and ACCF′=109.58° was found to fit the observed moments of inertia and to be consistent with determinations in other molecules. The primed Fs refer to fluorine atoms of the CHF2 group. Relative intensity measurements gave a torsional frequency of 74 cm−1 compared with the infrared observation of 73.4 cm−1. From these data, the barrier to internal rotation is 1223±34 cm−1 or 3.51±0.10 kcal/mole.

Microwave Spectrum, Dipole Moment, and Ring‐Puckering Vibration of β‐Propiolactone

The microwave spectrum of β‐propiolactone has been observed in the vibrational ground state and in the first four excited states of the ring‐puckering vibrational mode. The variation of the rotational constants with vibrational quantum number and the relative intensities of the observed vibrational satellites indicate that the vibration is essentially harmonic with ν0=160 cm−1 and with no appreciable barrier at the planar configuration. The dipole moment is 4.17±0.03 D, with μa=3.67±0.03 D, μb=1.99±0.02 D, and μc=0 in both the ground and first excited states.

Microwave Spectrum, Structure, and Dipole Moment of Cyclopropylphosphine

The microwave spectra of three isotopic species of cyclopropylphosphine have been analyzed. The conformation of the molecule is the symmetric one allowing maximum interaction of the lone pair electrons of phosphorus with the intra‐annular orbitals of the cyclopropyl ring. A structure compatible with the observed moments of inertia yields, along with other parameters, a C–P bond distance of 1.834 A, distinctly shorter than that observed in other organic phosphine derivatives. The dipole moment is found to be 1.16 D.

Microwave Spectrum, Barrier to Internal Rotation, Dipole Moment, and Structure of Trifluoromethylphosphine

The microwave spectra of CF3PH2, CF3PHD, and CF3PD2 have been observed and analyzed. The barrier to internal rotation is 2360 ± 80 cal/mole, approximately 400 cal/mole higher than the barrier in CH3PH2. The dipole‐moment components are μa = 1.77 ± 0.01 D, μc = 0.74 ± 0.03 D, and μtotal = 1.92 ± 0.02 D. The structural parameters are rC−P = 1.900 ± 0.006 A, rP−H = 1.43 ± 0.08 A, ∠FCF = 108.0 ± 0.4°, ∠CPH 91.9 ± 1.9°, and ∠HPH = 96.7 ± 1.8°. Compared with CH3PH2, the C‐P bond is significantly longer, ∠CPH is smaller, and ∠HPH is larger.

Solid State Microwave Spectrometer

A silicon solid state microwave spectrometer is described. It is more stable and reliable than comparable tube type circuits, is relatively low in cost, and produces a compact instrument. It is Stark‐modulated and can supply a Stark voltage of 2000 V into an external load of 1000 pF. The sweep generator employed is capable of electronic sweep durations of 0.1 to 8000 sec, using either a backward wave or reflex klystron oscillator signal source. The maximum sensitivity is limited only by the sample cell and detector noise.

Microwave Spectrum, Dipole Moment, and Ring‐Puckering Vibration of Vinylene Carbonate

The microwave spectrum of vinylene carbonate has been studied in the frequency region between 12 000 and 26 500 Mc/sec. Rotational constants and moments of inertia have been derived for the vibrational ground state and for the first three excited states of the ring‐puckering vibrational mode. The molecule is planar, with no barrier at the planar configuration in the ring‐puckering potential function. Measured intensities of the vibrational satellites are fitted well by a purely quadratic potential function. The dipole moment, which lies exclusively along the a axis, is 4.57±0.05 D.

An alternating pulsed magnetic field gradient apparatus for NMR self-diffusion measurements

Abstract An apparatus is described for the application of alternating pulsed magnetic field gradients for NMR self-diffusion measurements. In contrast with previous methods, this is done using a single set of quadrature coils and a single power supply. In addition, an NMR probe configuration is described which allows a gas flow temperature-regulated system along with the gradient coil to be placed within a 44-mm magnet gap. Some results and observations indicate that residual magnetic field gradients, which are produced by the pulsed gradients, are not due to induced eddy currents and are nonlinear. Calculations of the magnetic field gradient for a rotated gradient coil including image currents in the magnet pole faces are included. The effects of gradient coil orientation on anisotropic diffusion measurements in magic-angle-oriented systems are discussed.