Sub-Millimeter-Wave Spectroscopy of the Ar.H+3 and Ar.D+3 Ionic Complexes

Trihydrogen Cation Helium Clusters: A New Potential Energy Surface

We present a new analytical potential energy surface (PES) for the interaction between the trihydrogen cation and a He atom,H 3 + - H e ${{H}_{3}^{+}-He}$ , in its electronic ground state. The proposed PES has been built as a sum of two contributions: a polarization energy term due to the electric field generated by the molecular cation at the position of the polarizable He atom, and an exchange-repulsion and dispersion interactions represented by a sum of "atom-bond" potentials between the three bonds ofH 3 + ${{H}_{3}^{+}}$ and the He atom. All parameters of this new PES have been chosen and fitted from data obtained from high-level ab-initio calculations. Using this new PES plus the Aziz-Slaman potential for the interaction between Helium atoms and assuming pair-wise interactions, we carry out classical Basin-Hopping (BH) global optimization, semiclassical BH with Zero Point Energy corrections, and quantum Diffusion Monte Carlo simulations. We have found the minimum energy configurations of small He clusters doped withH 3 + ${{H}_{3}^{+}}$ ,H 3 + H e N ${{H}_{3}^{+}{\left(He\right)}_{N}}$ , with N=1-16. The study of the energies of these clusters allows us to find a pronounced anomaly for N=12, in perfect agreement with previous experimental findings, which we relate to a greater relative stability of this aggregate.

The He–H3+ complex. II. Infrared predissociation spectrum and energy term diagram

The rotationally resolved infrared (IR) spectrum of the He–[Formula: see text] complex has been measured in a cryogenic ion trap experiment at a nominal temperature of 4 K. Predissociation of the stored complex has been invoked by excitation of the degenerate ν2 mode of the [Formula: see text] sub-unit using a pulsed optical parametric oscillator system. An assignment of the experimental spectrum became possible through one-to-one correlations with bands of the spectrum theoretically predicted in Paper I [Harding et al., J. Chem. Phys. 156, 144307 (2022)]. 19 bands have been assigned and analyzed, and the energy term diagram of the lower states of this floppy molecular complex has been derived from combination differences (CDs) in the experimental spectrum. Ground state combination differences (GSCDs) reveal a large part of the energy term diagram for the He–[Formula: see text] complex in its vibrational ground state, v = 0. Experimental and theoretical term energies agree within experimental accuracy for the rotational fine structure associated with the total angular momentum quantum number J and the parity e/ f as well as for the coarse spacing of the lowest K states of the complex. This favorable comparison shows that the potential energy surface (PES) calculated in Paper I is accurate. The barriers between the three equivalent global minima in this PES are relatively low and the He–[Formula: see text] complex is extremely floppy, with nearly unhindered internal rotation of the [Formula: see text] sub-unit. The resulting Coriolis interactions couple the internal and end-over-end rotation of the complex and contribute significantly to the energy terms. They are observed both in experiment and theory and are, e.g., the origin of different rotational constants for states of e and f parity. Also in this respect, experiment and theory agree very well. Despite the assignment and analysis of many bands of the extremely rich IR spectrum of He–[Formula: see text], higher levels of excitation, including the complex stretching mode, need further attention.

Infrared spectroscopy and anharmonic theory of H3 +Ar2,3 complexes: The role of symmetry in solvation

The vibrational spectra of H₃ ⁺Ar_2,3 and D₃ ⁺Ar_2,3 are investigated in the 2000 cm^-1 to 4500 cm^-1 region through a combination of mass-selected infrared laser photodissociation spectroscopy and computational work including the effects of anharmonicity. In the reduced symmetry of the di-argon complex, vibrational activity is detected in the regions of both the symmetric and antisymmetric hydrogen stretching modes of H₃ ⁺. The tri-argon complex restores the D_3h symmetry of the H₃ ⁺ ion, with a concomitant reduction in the vibrational activity that is limited to the region of the antisymmetric stretch. Throughout these spectra, additional bands are detected beyond those predicted with harmonic vibrational theory. Anharmonic theory is able to reproduce some of the additional bands, with varying degrees of success.

Cationic Noble-Gas Hydrides: From Ion Sources to Outer Space

Cationic species with noble gas (Ng)-hydrogen bonds play a major role in the gas-phase ion chemistry of the group 18 elements. These species first emerged more than 90 years ago, when the simplest HeH+ and HeH2 + were detected from ionized He/H2 mixtures. Over the years, the family has considerably expanded and currently includes various bonding motifs that are investigated with intense experimental and theoretical interest. Quite recently, the results of these studies acquired new and fascinating implications. The diatomic ArH+ and HeH+ were, in fact, detected in various galactic and extragalactic regions, and this stimulates intriguing questions concerning the actual role in the outer space of the Ng-H cations observed in the laboratory. The aim of this review is to briefly summarize the most relevant information currently available on the structure, stability, and routes of formation of these fascinating systems.

High-Resolution Infrared and Millimeter-Wave Study of D(3)SiF: The Ground and v(3)=1 States of the (29)Si and (30)Si Species, and the v(3)=v(6)=1 and v(3)=2 States of D(3) (28)SiF

The nu(3) band of D(3)SiF near 890 cm(-1) recorded with a resolution of 2.4x10(-3) cm(-1) has been explored for the (29)Si and (30)Si isotopic species. Moreover, the nu(3)+nu(6)-nu(6) and 2nu(3)-nu(3) bands for the main (28)Si isotopomer have been assigned. For this purpose the nu(3)+nu(6) and 2nu(3) bands at 1435.697 and 1769.531 cm(-1) have been studied. Ground state parameters of the (29)Si and (30)Si species have been determined by merging newly measured MMW frequencies and ground state combination differences. In addition, v(3)=1 excited state parameters for these species have been obtained. While for the (28)Si species the v(3)=v(6)=1 state is locally perturbed by levels of the v(2)+v(5)=2 polyad, the v(3)=2 state appears to be unperturbed, its parameters being predictable from those of the v(3)=1 state. Anharmonicity constants x(33)=-4.1334 cm(-1) and x(36)=-3.6547 cm(-1) have been determined. Copyright 2001 Academic Press.

High-Resolution FTIR and Millimeter-Wave Study of D(3)SiF: The Ground, v(3) = 1, and v(6) = 1 and 2 States

The nu(6) (555.453 cm(-1)), the nu(3) (888.899 cm(-1)), and the very weak 2nu(6) infrared bands (2nu(-/+2)(6) 1101.734 cm(-1), 2nu(0)(6) 1100.102 cm(-1)) for the (28)Si species of D(3)SiF have been recorded with a resolution of 3.3, 2.4, and 5.0 x 10(-3) cm(-1), respectively. Millimeter-wave spectra up to 640 GHz of D(3)SiF in the ground, v(3) = 1, and v(6) = 1 and 2 states were measured. Ground state constants complete up to H constants including the K-dependent parameters A(0), D(0)(K), and H(0)(K) as obtained by the nu(+/-1)(6)/2nu(+/-2)(6)-nu(+/-1)(6)/2nu(-/+2)(6) loop method were determined by a merge of 2388 ground state combination differences with 59 rotational data. The v(3) = 1 and v(6) = 1 and 2 levels appear to be unperturbed intervibrationally for the J and K values that could be accessed. However, Deltal = Deltak = +/-2 and Deltal = +/-2, Deltak = -/+4 interactions affect the v(6) = 1 level while the v(6) = 2 levels undergo three interactions of Deltal = Deltak = +/-2, Deltal = +/-2, Deltak = -/+1 and Deltal = +/-4, Deltak = -/+2 type. Typically, for the different bands, 2000-4000 pieces of infrared data augmented by 36-120 rotational data were fitted together. Owing to the weakness of the 2nu(6) band, the body of v(6) = 2 data was enlarged by energies that are deduced from the 2nu(6)-nu(6) and nu(6) bands and which span in particular high K values. Comparison with available ab initio data derived from the harmonic and anharmonic force fields is made. Copyright 1999 Academic Press.