Buffer gas

About: Buffer gas is a research topic. Over the lifetime, 3565 publications have been published within this topic receiving 47283 citations.

Confinement narrowing and absorber speed dependent broadening effects on co lines in the fundamental band perturbed by xe, ar, ne, he and n2

Abstract: Lines of the CO fundamental band are studied at low concentration in He, Ne, Ar, Xe or N2 as buffer gas from 10 to 600 torr. The coefficient β0 associated with the Dicke narrowing effect is determined for each of the five mixtures. To obtain the proper value of this coefficient, when the pressure increases, the absorber speed dependence of the pressure broadening γ0 must be taken into account. Pressure shifts are also measured, and a faint asymmetry is observed for the COXe mixture. The line scanning is done with a TDL tightly controlled by a Michelson interferometer. A precision better than one-thousandth for absorbed intensity and a wavenumber precision of a few 10−5 is reached. These precisions were found necessary for the needed parameter measurements.

Experiment and theory for CO2 laser‐induced CF2HCl decomposition rate dependence on pressure and intensity

Abstract: A laser‐excited fluorescence method has been used to determine the rates at which CF2HCl molecules dissociate into CF2+HCl fragments during CO2 laser pulses of uniform fluence and known intensity. A study has been made of the dependence of the rate on CO2 laser intensity and pressure of Ar buffer gas from the collision‐free regime to atmospheric pressure. The effect of increasing Ar pressure is initially to increase the CF2HCl dissociation rate; above a moderate pressure (∼50 Torr), the rate is independent of Ar pressure up to atmospheric pressure. The data has been compared to a model, which adequately reproduces all the experimental data. The model treats the effect of collision between CF2HCl and the argon buffer gas in terms of rotational equilibration or ’’hole filling’’ in the discrete energy level region of CF2HCl. The discrete energy levels are interfaced to a quasicontinuum of vibrational–rotational states in a self‐consistent manner which incorporates a background of nonpumpable CF2HCl states as a finite heat bath interacting with the pump mode. The model is used to calculate the rate of formation of product CF2 molecules as a function of argon pressure and CO2 laser intensity. The quasicontinuum for CF2HCl is predicted to begin about four quanta above the ground state. The absorption cross section in the quasicontinuum is shown to decrease from 10−18 to 10−20 cm2 at V=15. The energy distribution in CF2HCl is predicted to be decidedly nonthermal both below and beyond threshold.

Low energy electron attachment to SF6 in N2, Ar, and Xe buffer gases

Abstract: The electron attachment rate constants ka for SF6 have been measured in dilute mixtures of SF6 in high pressure (>1 atm) N2, Ar, and Xe buffer gases at room temperature (T≊300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies 〈e〉 from near thermal electron energies (≊0.04 eV) to 〈e〉≊4.3 eV. Particular attention has been paid to the effects of space charge distortion, molecular impurities, and changes in the electron energy distribution function on the measured electron attachment rate constant values at the lower E/N values in these mixtures. The present measured thermal electron attachment rate constants in SF6/N2 and SF6/Xe gas mixtures are in excellent agreement with recent accurate measurements of these parameters in several SF6/buffer gas mixtures. At higher 〈e〉 values, the present SF6/N2 measurements are in fair agreement with previous measurements, while no previous measurements using Ar and Xe buffer gases have been published. T...

Efficient rotational cooling of Coulomb-crystallized molecular ions by a helium buffer gas

Abstract: In combination with sympathetic cooling of translational degrees of freedom (leading to Coulomb crystallization), cooling of the rotational degrees of freedom of magnesium hydride ions using a helium buffer gas leads to temperatures in a tunable range from 60 kelvin down to about 7 kelvin for a single ion, the lowest such temperature so far recorded. Cold molecules in quantities sufficient for study are in demand in a number of fields, ranging from fundamental physics to astrochemistry. Anders Hansen et al. demonstrate how a combination of techniques — helium buffer gas cooling (for internal rotational states) and 'sympathetic' collision cooling (for translational states) — can be used to achieve efficient cooling of molecular ions in all degrees of freedom. Most notable is the effectiveness of the technique for rotational cooling, which enhances the prospects for undertaking such studies on larger molecules. The preparation of cold molecules is of great importance in many contexts, such as fundamental physics investigations1,2, high-resolution spectroscopy of complex molecules3,4,5, cold chemistry6,7 and astrochemistry8. One versatile and widely applied method to cool molecules is helium buffer-gas cooling in either a supersonic beam expansion9,10 or a cryogenic trap environment11,12. Another more recent method applicable to trapped molecular ions relies on sympathetic translational cooling, through collisional interactions with co-trapped, laser-cooled atomic ions, into spatially ordered structures called Coulomb crystals, combined with laser-controlled internal-state preparation6,7,13,14,15,16,17,18,19,20,21,22,23. Here we present experimental results on helium buffer-gas cooling of the rotational degrees of freedom of MgH+ molecular ions, which have been trapped and sympathetically cooled13 in a cryogenic linear radio-frequency quadrupole trap. With helium collision rates of only about ten per second—that is, four to five orders of magnitude lower than in typical buffer-gas cooling settings—we have cooled a single molecular ion to a rotational temperature of kelvin, the lowest such temperature so far measured. In addition, by varying the shape of, or the number of atomic and molecular ions in, larger Coulomb crystals, or both, we have tuned the effective rotational temperature from about 7 kelvin to about 60 kelvin by changing the translational micromotion energy of the ions24. The extremely low helium collision rate may allow for sympathetic sideband cooling of single molecular ions, and eventually make quantum-logic spectroscopy25 of buffer-gas-cooled molecular ions feasible. Furthermore, application of the present cooling scheme to complex molecular ions should enable single- or few-state manipulations of individual molecules of biological interest4,5.

High-temperature alkali vapor cells with antirelaxation surface coatings

Abstract: Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 °C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 °C for both potassium and rubidium. We consider the experimental concerns of operating without buffer gas and with minimal quenching gas at high vapor density, studying the stricter need for effective quenching of excited atoms and deriving the optical rotation signal shape for atoms with resolved hyperfine structure in the spin-temperature regime. As an example of a high-temperature application of antirelaxation coated alkali vapor cells, we operate a spin-exchan...