Collision dynamics of polyatomic molecules containing carbon rings at low temperatures

Abstract

We explore the collision dynamics of complex hydrocarbon molecules (benzene, coronene, adamantane, and anthracene) containing carbon rings in a cold buffer gas of (3)He. For benzene, we present a comparative analysis of the fully classical and fully quantum calculations of elastic and inelastic scattering cross sections at collision energies between 1 and 10 cm(-1). The quantum calculations are performed using the time-independent coupled channel approach and the coupled-states approximation. We show that the coupled-states approximation is accurate at collision energies between 1 and 20 cm(-1). For the classical dynamics calculations, we develop an approach exploiting the rigidity of the carbon rings and including low-energy vibrational modes without holonomic constraints. Our results illustrate the effect of the molecular shape and the vibrational degrees of freedom on the formation of long-lived resonance states that lead to low-temperature clustering.

Collisional relaxation of vibrational states of SrOH with He at 2 K

“…From the measurement of τ 000 as a function of the helium density (figure 4(b)) using equation (2) agrees with the theoretical prediction for larger polyatomic molecules colliding with helium [31].…”

Non-sticking of helium buffer gas to hydrocarbons

“…This result is extremely encouraging for using helium as a buffer gas for cooling large biological molecules, which relies on helium buffer gas not sticking to the molecules. This result is in agreement with all empirical evidence [3,[7][8][9][10] and other theoretical calculations [11][12][13] based on classical trajectories. Our approach complements these calculations, enabling a rough survey of molecular species and their behavior in the buffer-gas environment.…”

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

“…On the other hand, the interaction of a closely-related molecule C 6 H 6 with He is well characterized and accurate quantum dynamical calculations of the cross sections for C 6 H 6 -He collisions have been previously reported [2,3]. This raises the question: given the cross sections for C 6 H 6 -He scattering is it possible to make predictions of the cross sections for C 6 H 5 CN -He collisions?…”

“…At the same time, the interaction of benzene (C 6 H 6 ) with He can be accurately described using a semi-empirical bond-additive method [23,24] and the cross sections for collisions of C 6 H 6 with He can be computed using an accurate coupled states approach [25,26] based on the time-independent quantum scattering theory [2]. In the present section, we show how the GP model can be used to obtain the range of the cross sections for He -C 6 H 5 CN collisions, given the cross sections for He -C 6 H 6 collisions.…”

“…Consider, for example, the collision properties of benzene C 6 H 6 and benzene substitutes C 6 H 5 -X, where X is a halogen atom or a molecular group. The D 6h symmetry of benzene reduces the numerical complexity of the quantum scattering calculations to a great extent [2]. The absence of this symmetry in C 6 H 5 -X makes the scattering calculations much more computationally difficult, often impossible.…”