Fluorescence excitation spectra of 1-methyl-, 2-methyl- and 2-ethyl-naphthalenes have been observed with the excitation of a xenon lamp in a supersonic free jet. The excitation spectrum of 1-methylnaphthalene was much the same with that of naphthalene, while 2-methyl- and 2-ethyl-naphthalene molecules exhibited entirely different spectral profile from 1-methylnaphthalene. Methylation or ethylation on the position 2 of naphthalene ring caused an increase of the origin intensity and changes of vibronic band frequency, which can be explained by symmetry reduction and mode mixing.

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For Hg I λ2537 Å (6³P→6¹S) line emitted from a low-pressure mercury lamp, we have determined the relative population in the upper level as a function of discharge current and mercury density. From the radial profile of the emission-line intensity, the spatial distribution function of the upper-revel population has been determined to be the zero-th order decay mode for the trapped radiation. Line absorption has been measured by a mercury vapor in a cell with various mercury densities and Lorentzian widths. The results are consistent with the upper-levl-population distribution as determined above. On the basis of these findings we calculate the emission-line profile and its change in the absorption cell. The amount of absorption at an arbitrary depth of the absorption cell is calculated, and the optium cold-spot temperature of the lamp of 40-50°C is suggested for the maximum absorption under the typical condition of the photo-CVD experiment.

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