Rovibrational calculations for CH3+–Rg (Rg=He,Ne): The prototype disk-and-ball dimer

Abstract

Experimental and theoretical investigation of the c 1 Π-a 1 Δ transition of NH/D-NeRovibrational calculations in the intramolecular ground vibrational states of the CH 3 ϩ -Rg dimers, RgϭHe and Ne, are carried out on intermolecular ab initio potential energy surfaces ͑PESs͒ calculated at the MP2 level of theory using a basis set of aug-cc-pVTZ quality. The internal CH 3 ϩ coordinates in the dimer are kept frozen at the optimal monomer coordinates ͑D 3h symmetry, rigid monomer approximation͒. The three-dimensional ͑3D͒ intermolecular PESs of both dimers feature pronounced global minima at p-bound equilibrium structures: the Rg atom is attached to one side of the 2p z orbital of the central C atom along the C 3 symmetry axis ͑C 3v symmetry͒. The intermolecular C-He and C-Ne bonds are characterized by separations of R e ϭ1.93 and 2.21 Å and dissociation energies of D e ϭ672 and 935 cm Ϫ1 , respectively. The PESs of these prototype disk-and-ball dimers reveal substantial angular-radial coupling in the region of the global minimum which leads to significant differences between the equilibrium and vibrationally averaged separations, R e and R 0 . The 3D rovibrational calculations on the rigid monomer PESs yield R 0 ϭ2.54 and 2.43 Å and D 0 ϭ193 and 474 cm Ϫ1 for CH 3 ϩ -He and CH 3 ϩ -Ne, respectively. In general, the spectroscopic constants derived for the ground vibrational states of both complexes are in good agreement with recent spectroscopic data obtained by infrared photodissociation spectroscopy.

Vibrational analysis of methyl cation - rare gas atom complexes: CH$_3^+$-Rg (Rg=He, Ne, Ar, Kr)

“…Based on calculations on a 3-dimensional energy surface of the interaction potential at the MP2 level (keeping all intramolecular coordinates of the CH + 3 moiety frozen), significant splittings were found for the bending and stretching modes in the CH + 3 -He complex and a splitting of about 0.008 cm −1 for the vibrational ground state. 4 In contrast to that recent studies by Töpfer et al based on double resonance rotational spectroscopy do not confirm this result. 9 Therefore, we will consider this aspect in some detail.…”

“…The spectroscopic investigation of ionic complexes is a challenging task and is usually accompanied by ab initio calculations to guide the interpretation of the observed spectra. [1][2][3][4][5][6][7] However, as these clusters are often very floppy, they request a proper account of anharmonic corrections and correlation effects in order to yield reliable results. Complexes of the methyl cation with rare gas atoms have extensively been studied by Dopfer and co-workers and a wealth of information is available for these systems.…”

“…Complexes of the methyl cation with rare gas atoms have extensively been studied by Dopfer and co-workers and a wealth of information is available for these systems. [1][2][3][4][5] These authors used infrared photodissociation spectroscopy in combination with ab initio calculations at the MP2 level with a modified aug-cc-pVTZ basis set to gain an understanding of the structural and vibrational properties of these complexes. Of course, 2nd order Møller-Plesset perturbation theory is limited in accuracy and predictions are often of qualitative rather than quantitative nature.…”

“…A particular aspect concerns tunneling splitting within these complexes. [1][2][3][4][5] As the dominant interaction within these complexes is associated with the 2p z orbital of the planar (D 3h ) methyl cation, the rare gas atom can be bound to either side of it. This results in two equivalent minima, which are mainly connected by a movement of the hydrogen atoms -rather than a large amplitude motion of the rare gas atom around the CH + 3 moiety.…”

Organohelium Compounds: Structures, Stabilities and Chemical Bonding Analyses

“…[28] Due to the high ionisation energy of He, this entity can be viewed as a neutral helium atom weakly interacting with CH 3 + , named a disk-and-ball complex. [29,30] This complex was found to have C 3v symmetry, with a CÀHe distance of 1.83 and a bonding energy of 2.02 kcal mol À1 at the MP2/aug-cc-pVTZ level. [4] The weakness of this interaction is due to the large energy difference between interacting orbitals: a pure p atomic orbital (AO) for CH 3 + and the 1 s AO of He (Figure 1, left side).…”