Exact bound rovibrational spectra of the neon tetramer

Abstract

Exact quantum dynamics calculations are performed for the bound rovibrational states of the neon tetramer (Ne4) in its ground electronic state, using pair-wise Lennard-Jones potentials and the ScalIT suite of parallel codes. The vibrational states separate into a low-lying group mostly localized to a single potential well and a higher-energy delocalized group lying above the isomerization threshold—with such a structure serving as a testament to the “intermediate” quantum nature of the Ne4 system. To accurately and efficiently represent both groups of states, the phase-space optimized discrete variable representation (PSO-DVR) approach was used, as implemented in the ScalIT code. The resultant 1D PSO effective potentials also shed significant light on the quantum dynamics of the system. All vibrational states were computed well up into the isomerization band and labeled up to the classical isomerization threshold—defined as the addition of the classical energy of a single bond, ϵ = 24.7 cm−1, to the quantum ground state energy. Rovibrational energy levels for all total angular momentum values in the range J = 1–5 were also computed, treating all Coriolis coupling exactly.

Computation and analysis of bound vibrational spectra of the neon tetramer using row orthonormal hyperspherical coordinates

“…This method was used in ref. 12 to obtain the full group IRREPs which the Ne 4 rovibrational states belong to from Jacobi coordinate calculations done for the IRREPs of the S 2 × S 2 subgroup, which contains 4 elements. In the present case, we could have generated the bound states for all S 3 IRREPs, not only Γ = A 31 which contains the physically allowed states, but also for Γ = A 32 and Γ = E (3) .…”

“…it is the one of the LHSF subset on which it has non zero expansion coefficients. Neon is a boson with zero nuclear spin and the only physically relevant bound states belong to the full group IRREP A Our convergence goal is to obtain bound state energies within 1 % of the reference data given by [12] and which turn out to be fully converged. This objective was achieved by choosing a truncated harmonic basis set such that n ≤ n max =50 and L ≤ L max =30 for…”

“…A splitting of the Ne 4 vibrational spectrum in 3 regions is proposed in ref. [12]. It is based on the analysis of the increase of the tunneling splittings and of the density of vibrational states (DOS) with energy.…”

“…11, the second one the full rovibrational spectrum computation of Ne 4 described in ref. 12. The recent availability of these latter Ne 4 spectra provides a good opportunity to test for the first time the capability of the hyperspherical coordinate method to obtain the vibrational spectrum of a tetratomic system beyond the drastic adiabatic approximation.…”

“…In section III, we first present the obtained vibrational spectra and we discuss their accuracy by comparison with the reference data of ref. [12]. Then, we describe the physical insight provided by the hyperspherical method : we present the LSHF energy curves as a function of ρ (subsection III B), the LHSF themselves (subsection III C) and the bound states (subsection III D).…”