Buffer Gas Helium Research Articles

Rotational relaxation of fluoromethane molecules in low-temperature collisions with buffer-gas helium

We propose a method to study the rotational relaxation of polar molecules [here taking fluoromethane $({\mathrm{CH}}_{3}\mathrm{F})$ as an example] in collisions with 3.5 K buffer-gas helium (He) atoms by using an electrostatic guiding technique. The dependence of the guiding signal of ${\mathrm{CH}}_{3}\mathrm{F}$ on the injected He flux and the dependence of the guiding efficiency of ${\mathrm{CH}}_{3}\mathrm{F}$ on its rotational temperature are investigated both theoretically and experimentally. By comparing the experimental and simulated results, we find that the translational and rotational temperatures of the buffer-gas cooled ${\mathrm{CH}}_{3}\mathrm{F}$ molecules can reach to about 5.48 and 0.60 K, respectively, and the ratio between the translational and average rotational collisional cross sections of ${\mathrm{CH}}_{3}\mathrm{F}\ensuremath{-}\mathrm{He}$ is $\ensuremath{\gamma}={\ensuremath{\sigma}}_{t}/{\ensuremath{\sigma}}_{r}=36.49\ifmmode\pm\else\textpm\fi{}6.15$. In addition, the slowing, cooling, and boosting effects of the molecular beam with different injected He fluxes are also observed and their forming conditions are investigated in some detail. Our study shows that our proposed method can not only be used to measure the translational and rotational temperatures of the buffer-gas cooled molecules, but also to measure the ratio of the translational collisional cross section to the average rotational collisional cross section, and even to measure the average rotational collisional cross section when the translational collisional cross section is measured by fitting the lifetime of molecule signal to get a numerical solution from the diffusion equation of buffer-gas He atoms in the cell.

Overtone spectroscopy of water molecules based on room temperature diode laser emitting in the NIR range

The measurement of very weak overtone spectroscopic line shape of water molecule is performed using wavelength modulation spectroscopy (WMS). In this work a high resolution near infrared diode laser spectrometer is used to record first derivative (1f) signal of buffer gas Helium and Carbon dioxide broadened water vapour transitions around 820 nm wavelength region. The effect of collision due to perturber pressure on signal to noise ratio (SNR) is discussed. The Lorentzian HWHM of observed 1f signal is calculated. The comparison is made between collisional broadening of water vapour transition broadened by inert gas Helium and high quadrupole moment active gas Carbon dioxide.

Effect of Na–Na spin-exchange collisions on spin relaxation of optically pumped Na in Xe gas

We report the first detection of the effect of Na–Na spin exchange collisions on spin relaxation of optically pumped Na in Xe gas by studying the relaxation in the "dark" of the variable ⟨Sz⟩ in a mixture of dense sodium vapor (number density [Na] ~ 1013 cm−3), and buffer gas helium, xenon and nitrogen as a function of [Na] and xenon pressure.