Cooling and collisions of large gas phase molecules

Abstract

The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters. Cold and dense samples of naphthalene (C 10 H 8 ) are produced using buffer gas cooling in combination with rapid, high flow molecule injection. The observed naphthalene density is n E 10 11 cm À3 over a volume of a few cm 3 at a temperature of 6 K. We observe naphthalene-naphthalene collisions through two-body loss of naphthalene with a loss cross section of s N-N = 1.4 Â 10 À14 cm 2 . Analysis is presented that indicates that this combination of techniques will be applicable to many comparably sized molecules. This technique can also be combined with cryogenic beam methods 1 to produce cold, high flux, continuous molecular beams.

The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules

“…The buffer gas cooling technique works by dissipating the energy of the species of interest via elastic collisions with cold, inert gas atoms, such as helium or neon. Since this cooling mechanism does not depend on the internal structure of the species (unlike laser cooling), buffer gas cooling can be applied to nearly any atom or small molecule [4], and certain large molecules [57]. Helium maintains a sufficient vapor pressure down to a few hundred mK [4,58], and the typical helium-molecule elastic cross section [4] of ∼ 10 −14 cm 2 allows buffer gas cool- ing and trap loading to be realized with modest cell sizes (few × few × few cm 3 ).…”

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

“…While the distribution in Figure 1 is only applicable to the initial collisions, as it applies to an unphysical homogeneous mixture of molecular gas and buffer gas at two very different temperatures, it provides an indicative experimental collision energy range of 0-150 cm 1 . As such, the collisional energy transfer between all symmetry-and energy-allowed transitions is considered at collision energies from 0.1 cm 1 to 150 cm 1 , in accordance with the experimental parameters.…”

“…As detailed in two recent publications, 10,11 quantum closecoupling calculations have been performed to establish inelastic cross sections for the collisions of NH 3 with He at a range of collision energies, spanning 0.01-150 cm 1 . The cross section calculations are carried out with the close-coupling method using the four-dimensional potential energy surface (PES) developed by Gubbels et al 12 The four dimensions of the PES comprise the three spherical coordinates of He relative to NH 3 and the NH 3 umbrella (or inversion) angle.…”

“…As such, buffer gas cooling methods are very versatile, requiring only that the species of interest be generated in the gas phase and that the formation of clusters is hindered. 1,2 With a range of techniques developed to produce gas-phase species in the buffer gas cell-including capillary filling, laser ablation, beam injection, and discharge etchingbuffer gas cooling has been successfully applied to numerous atomic and molecular systems. 3,4 Within a buffer gas cell, the molecules of interest undergo elastic and inelastic collisions with a cold buffer gas such as helium.…”

Gaussian process model for extrapolation of scattering observables for complex molecules: From benzene to benzonitrile

“…Second, it is often necessary to compare the collision properties of different molecules for calibrating the experimental observations and/or the design of new experiments [5][6][7]. However, the direct measurements for some molecular species may often be difficult or impossible.…”