Krypton resonance lamps

Our experimental techniques have been described extensively in earlier papers (2, 13). The gamma ray irradiations were carried out in a 50,000-curie source located at the bottom of a pool. The photoionization experiments were carried out by krypton and argon resonance lamps of high purity. The krypton resonance lamp was provided with a CaF2 window which transmits only the 1236 A. (10 e.v.) line while the radiation from the argon resonance lamp passed through a thin ( 0.3 mm.) LiF window. In the latter case, the resonance lines at 1067 and 1048 A. are transmitted. The intensity of 1048-A. line was about 75% of that of the 1067-A. line. The number of ions produced in both the radiolysis and photoionization experiments was determined by measuring the saturation current across two electrodes. In the radiolysis, the outer wall of a cylindrical stainless steel reaction vessel served as a cathode while a centrally located rod was used as anode. The photoionization apparatus was provided with two parallel plate nickel electrodes which were located at equal distances from the window of the resonance lamp. 

Tanaka and Steacie411 photolyzed NO using the 1236-A line of a krypton resonance lamp. They measured the current produced and found that it increased if krypton was added to the NO. They interpreted this as a krypton-photosensitized ionization, the krypton absorbing its own radiation more than the NO. 

Fig. 4. Comparison of emisson of a krypton resonance lamp with getter (-----)...

Current-voltage saturation curves for krypton resonance lamps were determined in a special cell with two internal rectangular (1.1 X 1.7 cm.) nickel electrodes 1.6 cm. apart. The LiF window extended between the electrodes. For 1.3 torr NO the saturation current was typically about 2.5 fiamp. The lamp intensities were usually about 1015 quanta/sec. Lamp intensities were monitored at about 10 hour intervals of operation. 

Added Rare Gases. Added rare gases can collide with the gas phase ions and de-excite any excited ions. The effect of added argon and neon on the C8 product distribution is shown as a function of rare gas pressure in Table IV. Krypton was not used because it would absorb the photons from the krypton resonance lamp. Neon has little effect on the C8 product distribution, but argon causes the C8 products with a 2,2,4-structure to increase relative to the C8 products with a 2,2,3-structure. 

Nature of Ion Injected into Liquid Isobutylene. The krypton resonance lamp emits photons at 1236 A. (10.0 e.v.) and 1165 A. (10.6 e.v.) with relative intensities of 1.00 and 0.28 respectively (5). The ionization potential of isobutylene is 9.4 e.v., and the lowest appearance potential for a fragment ion from isobutylene is 11.3 e.v. (C4H7+) (I). Therefore, the only ion produced is the parent C4H8+. 

The vacuum ultraviolet photolysis source was a krypton resonance lamp, constructed with some modifications according to the design of workers at the National Bureau of Standards (22, 29). This lamp, fitted with lithium fluoride windows, was sealed directly to the reaction vessel whose volume was ca. 50 cc. The spectral emission of the lamp was examined with a scanning monochromator of the Seya-Namioka type. Some 75% of the emission in the region 1000-1600 A. was found to consist of the 1236-A. line. All photolysis experiments were carried out with a sample pressure of 40 mm. Hg. In addition to the 1236-A. line,... 

A photoionization system usually consists of a windowless, differentially pumped rare gas resonance lamp coupled with the ionization chamber of the mass spectrometer. Argon, krypton, or other inert gases are used in the lamp. Energies of 11.6 and 11.8 (Ar I) eV are produced by argon, and 10.0 and 10.6 (Kr I) eV for krypton. The pressure inside the ion source is usually about 10 Torr. 

The spectral output from several used lamps was examined on a McPherson vacuum ultraviolet monochromator. Strong krypton resonance lines were observed at 1236 A. and 1165 A. with relative intensities of about 4 to 1 respectively. A number of much weaker lines at longer wavelengths were observed which were mostly attributable to H20. Some H20 was apparently released from the borosilicate glass walls during the operation of the lamp. As will be seen later a weak lamp intensity at wavelengths longer than 1236 A. does not affect the ion chemistry of the isobutylene system. 

Table IV gives the relative product distribution from the vacuum ultraviolet photolysis of ethyl chloride at 40 mm. pressure using the 1236-A. krypton resonance line. Owing to the low intensity of emission from the resonance lamp, higher pressures were not used in the photolysis experiments in order to prevent the major portion of the reaction from occurring in the region of the window where surface interactions are likely. Therefore, to provide a basis for more direct comparison between the photolytic and radiolytic yields, the radiolysis of ethyl chloride was also examined at 40 mm. pressure. The relative yields from several experiments of the latter study are given in Table IV. The lowest conversion yields from the radiolysis at the lower pressure show a relative distribution which is in close agreement with the relative product distribution detected from the radiolysis at 357 mm. Therefore, there is no substantial pressure effect on the decomposition product yields in ethyl chloride over the range 40-357 mm.

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