Kurt Dressler

Radiative Lifetimes of Ultraviolet Molecular Transitions

Radiative lifetimes of UV molecular transitions, analyzing emission spectrum in vacuum monochromator

Absolute oscillator strengths of the strongest bands within the dipole-allowed absorption spectrum of nitrogen.

The absolute absorption f values of four bands of N2 in the 958‐972‐A region, b 1Πu–X (3–0, 4–0), l 1Πu–X, and p′ 1Σu+–X (0–0), have been determined using a 3‐m spectrometer as absorption cell with N2 gas pressures in the 10−6−10−4‐torr range, using the helium continuum with differential pumping, and double‐beam, windowless photoelectric recording with pulse‐counting electronics. More than 10 times narrower spectral bandwidth (0.04 A) was realized than previously reported in photoelectric absorption work at these wave‐lengths, thus enabling work down to more than 100 times smaller numbers of absorbing molecules. The consequent reduction of the effects of line saturation made possible the evaluation of absolute f values which are compared with other absolute and relative determinations from lifetime and electron impact measurements.

Infrared Spectroscopic Evidence for the Rotation of the Ammonia Molecule in Solid Argon and Nitrogen

High‐resolution infrared spectra (of the symmetric bending mode) of ammonia suspended at high dilution in solid argon and nitrogen have been obtained. More than a half dozen extremely sharp bands have been observed in the 950–1040 cm—1 region (in the spectrum of ammonia) in these materials under conditions where there should be little if any absorption due to polymeric species. The frequency separations of the bands, their temperature dependence, and their extreme sharpness appear to be compatible with a model in which the ammonia molecule executes quantized rotation in these solids.

Radiative Lifetimes of Ultraviolet Emission Systems Excited in BF3, CF4, and SiF4

Radiative lifetimes in the range 2 to 11 nsec have been measured by the phase‐shift method of Lawrence for four extensive near‐ and vacuum‐ultraviolet emission systems excited by 200‐V electrons in low‐pressure BF3, CF4, and SiF4 gases. With the possible exception of the system excited in BF3, the systems appear continuous under 0.4−A resolution and all are probably due to polyatomic emitters. Electron excitation spectra of several other gases are briefly described.

Apriori calculation of the vibron band and of the vibron–phonon and two‐phonon combination bands in the Raman spectrum of solid α‐N2

The observed shift, splitting, and intensity ratio of the vibrational Raman band in solid α‐nitrogen as reported by Anderson et al. have been reproduced in a calculation which is based on the quadrupole moments and polarizabilities of N2 in the gas phase. Furthermore, the intensities and shapes of the weak phonon sideband in the N2 stretching region, as well as of the two‐phonon sideband in the lattice region, have been calculated by treating these as combination bands which derive their intensities from electrical anharmonicities, i.e., from quadratic dependences of the polarizability on internal and external nuclear displacements. The contributions from mechanical anharmonicities, i.e., from vibron–phonon coupling through third and higher order terms in the vibrational potential, are found to be negligible in these band intensities. The computations of the lattice dynamics are based on a Lennard‐Jones plus quadrupole–quadrupole potential.

Absolute transition probabilities in the ultraviolet spectrum of co.

UV spectrum of CO molecule, determining absolute transition probabilities from radiation lifetime and relative radiation branching ratio

Photomultiplier Tube Pulses Induced by γ Rays

Background noise produced by high energy radiation incident on photomultiplier tube, stressing differences between tubes in number of small pulses produced