A Cryogenic Cell for Liquid Noble Gases. Vibrational Spectroscopy and Photochemistry of Transition Metal Carbonyls in Liquid Xenon

Abstract

The construction of a special cryogenic cell for spectroscopic and photochemical measurements in liquefied noble gases under pressure is described. The inner (sample) cell, withstanding a pressure of at least 700 psi, has no high-vacuum around it. It has two crossed IR and UV-visible optical pathways of 30 mm. The usefulness of these noble gases in vibrational spectroscopy is demonstrated for the following transition metal carbonyls, dissolved in liquid xenon (=LXe, pressure 6], [Mn₂(CO)₁₀l, and [Co₂(CO)₈]. The great advantage of LXe is its complete transparency over a wide spectral range. The limited solubility of many complexes in LXe in comparison with “normal” solvents is often compensated by the long optical pathway of the cell. Because of its complete inertness, reactive intermediates and products of photochemical reactions can be stabilized in LXe, even at moderate temperatures. The photochemical reaction is described of [W(CO)₆] with a l,4-diaza-l,3-butadiene (=R-DAB; RN=CHCH=NR) ligand. During this reaction a photoproduct is identified as a stable complex which is so unstable in normal solvents that it can only be observed with rapid-scan FT-IR spectroscopy.