I. The Rate of Recombination of Iodine Atoms. II. Some Studies of the Trace Quantities of Lead, Uranium, and Thorium in Marine Carbonate Skeletons

Year: 1955 DOI: 10.7907/KV4S-PC49
PART I.

The rate constants for the homogeneous recombination of iodine atoms in the gas phase I+I+M → d[I₂]/d[I₂][M], have been measured for the gases M=A, n̲e̲o̲-C₅H₁₂ and n̲-C₅H₁₂ at room temperature. The rate constants are 4.2 (±0.4) x 10⁹, 58 (±4) x 10⁹, and 65 (±6) x 10⁹ liter²mole⁻²sec⁻¹, respectively. In these experiments and those with iodine solutions, a short, intense pulse of light from a flash lamp dissociated 1-10% of the iodine molecules in a reaction cell. The photoelectric cell response to a light signal modulated with the change in the iodine atom concentration was amplified and used as the vertical deflection input of an oscilloscope. The oscilloscope trace, a direct indication of the subsequent recombination observed during periods from 0.0002 sec after the flash to as long as 0.01 sec, was recorded photographically.

The rate constants for the recombination of iodine atoms in the liquids CCl₄ and n̲-C₇H₁₆, d[I₂]/d[I₂], were found to be at room temperature 0.7 (±0.11) x 10¹⁰ and 2.2 (±0.4) x 10¹⁰ liter mole⁻¹sec⁻¹, respectively. The primary quantum yields in the solutions were found to 0.19 (±0.05) and 0.41 (±0.26), respectively.

PART II.

A procedure is described for the chemical isolation from carbonates of microgram quantities of lead, uranium, and thorium suitable for mass spectrometric analyses. The concentration of lead in a Jurassic belemnite as well as a Mississippian Spirifer has been found to be less than 1 ppm while for Strombus gigas, a living species of gastropod, the value 0.19±0.04 ppm was found. The uranium concentration in this gastropod was determined as 0.036±0.002 ppm. The isotopic composition of the lead from the Strombus gigas has also been determined and is compared to other analyses of "common" lead.