Quasistructural molecules

Abstract

The concept of quasistructural molecules is introduced. For quasistructural molecules (a) the notion of a static equilibrium structure, corresponding to a minimum on the potential energy surface of the molecule, loses its strict meaning, (b) internal

The rovibrational Aharonov-Bohm effect

“…First-principles characterization of the dynamics of H + 5 , as well as of its deuterated derivatives, has been achieved and it offered a number of considerable surprises. [25][26][27] As shown below, the rovibrational Aharonov-Bohm effect dominates the low-energy nuclear dynamics of this quasistructual 28 molecular ion, which is approximately a symmetric top with a nearly-free torsional motion.…”

“…Our starting point is the reduced-dimensionality 1D(φ) torsion model 25,26,28 developed to understand the low-energy quantum dynamics of H + 5 . The equilibrium structure of H + 5 is depicted in the left panel of Fig.…”

“…To illustrate this point further, in Table 1 we reproduce numerical results from Ref. 28 for the full 1D(φ) torsion model, compared with our perturbation theory analysis of the symmetric-top (Aharonov-Bohm) approximation. For this comparison, we need parameter values.…”

Exactly solvable 1D model explains the low-energy vibrational level structure of protonated methane

“…Over the last two decades [5], CH + 5 has been posing a formidable challenge to highresolution spectroscopists [5][6][7][8][9][10][11][12][13][14][15]. The most outstanding issue is that the spectrum of CH + 5 is exceptionally complex even at extremely low temperatures [9,13] due to its quasistructural nature [16].…”

On neglecting Coriolis and related couplings in first-principles rovibrational spectroscopy: considerations of symmetry, accuracy, and simplicity

“…Since variational computation [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] of rovibrational energy levels utilizing VR Ĥ are expensive, both in terms of memory and CPU time, it is highly useful that the rotational quantum number J is a good quantum number 20 and thus the matrix representation of Ĥ VR is block-diagonal in J. Then it is natural to consider KEO approximations that separate rotational and vibrational motions within these blocks in some form. Ideally, such approximations would apply to molecules with complicated internal motion [21][22][23][24][25][26][27][28][29] , as well as to semirigid ones. Hereby we explore in a joint analytical and numerical treatment-for the first time to our knowledge-the impact on accuracy and numerical efficiency that results when T VR  is neglected, employing different vibrational coordinates and different embeddings of the molecule-fixed axes.…”