Structured photoionization continuum of superheated cesium vapor

Abstract

We studied the absorption spectrum of dense cesium vapor in an all-sapphire cell with a special emphasis on the highly structured photoionization continuum. This continuum appears to be composed of atomic and molecular contributions which can be separated by means of additional superheating of the cesium vapor in the sapphire cell. This was possible due to the small amount of cesium filling which completely evaporated at a temperature of around 450 °C. This enabled the overheating of cesium dimers which greatly reduced its concentration at a temperature of 900 °C, leaving almost pure atomic Cs vapor. The analysis of the thermal destruction indicated that the highly structured molecular component of the photoionization continuum can be entirely attributed to cesium dimers. We discuss the possible origin of the structured photoionization continuum as stemming from the absorption process from the ground state of the Cs2 molecule to the doubly excited Cs2** molecule located above Cs2+ molecular ionization limit. The corresponding potential curves are subjected to mutual interactions and autoionization.

Superheating effects in line broadening of dense alkali vapors

“…Previous TOF work [4] already firmly established molecular origin of 245 and 270 nm photoionization bands. This experiment did not enable superheating separation process within present rubidium vapor conditions as previously performed in the case of cesium vapor [1]. However, since the ratio of [Rb2]/[Rb] densities increases with increasing temperature it is clear that at elevated temperatures photoionization bands of Rb2 become better visible in the spectrum.…”

“…A much more detailed description of the absorption photoionization measurements with superheated cesium vapor is given in ref. [1].…”

“…The superheating of the dense alkali vapor enables clear separation of atomic from the molecular photoionization spectrum [1]. The molecular photoionization continuum structure is about two orders of magnitude stronger than the atomic photoionization continuum [2].…”

Cs2‘diffuse bands’ emission from superheated cesium vapor

“…The cell was completely enclosed and isolated except for two small openings for collection of emitted light and light transmission measurements. An all-sapphire cell containing a very small droplet of cesium [5] was heated to temperatures up to 1000 °C (figure 1). The emission spectrum from the cell was acquired using an OceanOptics spectrometer (HR4000CG-UV-NIR) with QP600-2-VIS-NIR fiber.…”

“…One of the main purposes in many experiments was to get rid of the molecular contribution in the spectrum and to observe pure atomic spectral phenomena. Recently, superheating with effective thermal destruction of molecules was used to study structured photoionization continuum of the cesium vapor [5] in which both atomic and molecular contributions were present at diverse fractions at different temperatures. From the molecular destruction behavior, at superheated conditions, it was possible to extract the pure molecular contribution to the photoionization process of Cs 2 .…”