Robert C. Hirt

Near Ultraviolet Solution Spectra of the Diazines

The near ultraviolet spectra of the diazines and various derivatives have been obtained in several solvents. Intensities, contours, and positions of the observed bands are combined with a valence‐bond treatment of the diazine π‐electrons to assign the transitions and to evaluate the C–C and C–N exchange integrals. The diazine band near 30,000 cm−1 (3333A) is assigned to a nonbonding nitrogen electron transition, and the band near 40,000 cm−1 (2500A) to a π‐electron transition.

Ultraviolet Absorption Spectra of Derivatives of Symmetric Triazine. I. Amino Triazines

The near ultraviolet solution spectra of twenty one mono‐, di‐, and triamino derivatives of symmetric triazine are reported. The addition of amino groups to the s‐triazine ring introduces electrons which can interact with those of the ring, with resultant changes in the intensity and position of the absorption bands. The spectra of mono‐, di‐, triamino‐s‐triazine may be arranged in a Platt sequence along with that of trichloro‐s‐triazine and that expected for s‐triazine.

Near Ultraviolet Absorption Spectra of Melamine and Some Related Compounds

An absorption band of low intensity has been found in the 2800 to 3400A region for solutions of melamine, trimethylol melamine, trimethyl ether of trimethylol melamine, hexamethylol melamine, and cyanuric chloride. The band has also been observed in gaseous melamine at elevated temperatures. The band is believed to be due to a singlet‐triplet transition, rather than analogous to the 2600A absorption system of benzene.

Spectroradiometer–Luminometer for Chemiluminescence and Fluorescence Quantum-Yield Studies

A spectroradiometer–luminometer has been constructed, calibrated, and applied to the measurement of fluorescence- and chemiluminescence-emission intensity as a function of wavelength and to kinetic decay studies. It is also applicable to investigations of phosphorescence, electroluminescence, bioluminescence, and the spectroradiometry of external light sources. A computer program has been set up to take care of wavelength-response corrections and to convert emission intensities into photochemical, radiometric, or luminous units, including total integrated intensities for quantum-yield studies.

Ultraviolet absorption spectra of derivatives of symmetric triazine—III The guanyl-melamines

Abstract The ultraviolet absorption spectra of mono-, di- and tri-guanylmelamines, phenylguanylmelamine and phonylguanidine, and their ions have been determined. The ionization constants were measured by use of the “Spectro-Titrimeter”. The spectra and structures which have been assigned are consistent with other derivatives of symmetric triazine. The un-ionized forms are assigned structures having the guanidino-group carbon-nitrogen double bond in conjugation with the triazine ring; this conjugation is lost in the ionic forms.

A Continuous-Flow Method for Determining Dissociation Constants by Ultraviolet Spectrophotometry

The ultraviolet absorption spectra of organic compounds which have an acidic or basic functional group as an integral part of the chromophoric system will generally be pH-dependent; that is, the form and intensity of the absorption curve will change as the hydrogen ion concentration changes. This property may be utilized in the determination of dissociation constants of an acid or base by spectrophotometry.

Solarization studies on polyester resins using a heliostat-spectrometer

Abstract Natural sunlight has the photochemical effect referred to as “solarization” on polyester resins, producing yellowing as well as causing undesirable changes in other physical properties. The question of what wavelengths in the ultraviolet portion of the solar spectrum are responsible for the solarization has gone unanswered for lack of experimental data. It was decided to study the solarization of polyester resins using natural sunlight and to measure the conditions as closely as possible during exposures. A heliostat was constructed to send a beam of sunlight into a fast optical system consisting of a concave mirror and a quartz prism monochromator. The ultraviolet portion of the solar spectrum was spread across the resin sample which was in the focal plane of the spectrometer. The “activation spectrum” is the degree of yellowing as a function of incident wavelength as determined by densitometering the resin sample with monochromatic blue light. Polyester resins which were cross-linked with polystyrene were studied. The dibasic acids present were varied among phthalic plus maleic, adipic plus maleic, succinic plus maleic, and all maleic. Virtually identical activation spectra were obtained for the formulations, with maxima near 3300 A. Plots of yellowing versus the logarithm of the exposure gave straight lines, showing that, for monochromatic light, the resins obeyed the classic Hurter-Driffield law of photographic materials. Inertias and slopes were nearly the same for all formulations. In cases where the samples were solarized at very high rates, a dark reaction was observed following exposure which caused a fading of the yellowing. This may be interpreted as the destruction by oxygen of trapped free radicals.

Time-Lapse Emission Spectra Using a Rotating Slotted Disc and Stationary Emulsion

The construction, use, and advantages of a slowly rotating slotted disc at the slit of a stigmatic spectograph are described and illustrated in the production of time-lapse spectograms.

Ultraviolet Spectrophotometric Determination of Polystyrene in Polybutadiene

Polybutadiene samples may be analyzed by a refractive-index method, except at low levels of polystyrene—where the method becomes insensitive due to the very small changes in refractive index. Small concentrations of polystyrene are sometimes encountered in polybutadiene, in the range of 5% or less. These levels of polystyrene may be detected and determined by ultraviolet spectrophotometric examination of samples of sheets prepared from the latex by the ASTM procedure. These sheets are translucent, but are insoluble in the usual ultraviolet-transparent solvents. It was found that the sheet samples become transparent upon compression. The sample was placed between the internal surfaces of the quartz windows of a micrometer Baly cell and compressed by turning the micrometer screw. The polystyrene content was determined from the absorbance at 269 mμ, as measured on a Cary model 11 or 14 recording spectrophotometer.