Efficient cooling in supersonic jet expansions of supercritical fluids: CO and CO2

Abstract

Pulsed, supersonic beams of pure carbon monoxide and carbon dioxide at stagnation conditions above their critical point have been investigated by time-of-flight measurements as a function of pressure and temperature. Although both molecules form clusters readily in adiabatic expansions, surprisingly large speed ratios (above 100) indicative of very low translational temperatures (below 0.1 K) have been achieved. In particular, the supersonic expansion of CO(2) at stagnation temperatures slightly above the phase transition to the supercritical state results in unprecedented cold beams. This efficient cooling is attributed to the large values of the heat capacity ratio of supercritical fluids in close vicinity of their critical point.

Collisional cooling of ultracold molecules

“…Buffer gas cooling [10] cannot push below 100 mK due to the rapidly diminishing vapor pressure of buffer gases (even 3 He) at such temperatures. Supersonic expansion [11] can produce temperatures around 100 mK. Controlled collisions in crossed molecular beams [12] can in principle reduce this temperature further, though the technique hasn't been demonstrated below 400 mK.…”

Simple and compact nozzle design for laser vaporization sources

“…Flight Time (μs) Figure 3. Time-of-flight profile for AlH with temperature fit from [25]. Error bars correspond to 1σ confidence intervals for a Poisson process.…”

Ultra-precise particle velocities in pulsed supersonic beams

“…[83][84][85][86] One of the numerous interesting questions in this context is the fate of the condensation energy that is released during cluster formation, which may show up in an increased flow velocity or an increased cluster temperature.…”