Electron spin resonance study on H6+, H5D+, H4D2+, and H2D4+ in solid parahydrogen

Abstract

We carried out an electron spin resonance (ESR) study on hydrogen ion radicals produced by radiolysis of solid para-H(2). In addition to quartet ESR lines proposed to be H(2) (+)-core H(6) (+) (D(2d)) ions in solid para-H(2) [T. Kumada et al., Phys. Chem. Chem. Phys. 7, 776 (2005)], we newly observed totally more than 50 resolved lines in gamma-ray irradiated solid para-H(2)-ortho-D(2) (1 mol %) and para-H(2)-HD (1 mol %) mixtures. We assigned these lines to be isotope substituents of H(2) (+)-core H(6) (+) ions such as H(5)D(+), H(4)D(2) (+), and H(2)D(4) (+) throughout the comparison of their ESR parameters with theoretical results. These results provide a conclusive evidence that H(2) (+)-core H(6) (+) ions are generated in irradiated solid hydrogens. Analysis of the EPR spectrum and ab initio calculations predicts D(2d) symmetry of the H(6) (+) ions, whereas a lowering symmetry (D(2d)-->C(2v)) induced by asymmetric nuclear wave function is observed in H(5)D(+) and H(4)D(2) (+). We also observed isotope-substitution reactions such as H(6) (+)+D(2)-->H(4)D(2) (+)+H(2) and H(6) (+)+HD-->H(5)D(+)+H(2), which are analogous to the well-known isotope-condensation reactions of H(3) (+) in dark nebula, H(3) (+)+HD-->HD(2) (+)+H(2) and HD(2) (+)+HD-->D(3) (+)+H(2).

Formation of even-numbered hydrogen cluster cations in ultracold helium droplets

“…The D 2d structure has been confirmed in an electron spin resonance study of hydrogen ion radicals produced by radiolysis of solid parahydrogen. 79 The two outer H 2 molecules were found to rotate almost freely, in agreement with a path integral molecular dynamics study. 80 We have searched the H 6 + potential energy surface for other possible isomers that might serve as cores for the coordination of additional H 2 molecules.…”

“…Although the thermodynamic stability of even-numbered hydrogen cluster ions already was pointed out by Wright and Borkman 72 in 1982, these species have, with the exception of H 6 + , 53,79 largely escaped experimental identification. The main reason for the difficulty of identifying even-numbered H n + in mass spectra of hydrogen clusters is the fact that a large fraction of the energy that is released upon vertical ionization is transferred to a hydrogen atom that will thus leave the ionized complex within Ͻ1 ps.…”

Non-Born-Oppenheimer potential energy curve: Hydrogen molecular ion with highly accurate free complement method

“…We will further extend the accurate non-BO applications of the FC method to a more general molecule in future studies. As an example, hydrogen clusters, which are an important species in astrochemistry and lowtemperature physics, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] should include a lot of complicated local minimums in their PECs and the present methods are worth applying to them. Exotic systems including particles lighter than protons are also interesting for a more significant non-BO effect.…”

Negative and positive ion trapping by isotopic molecules in cryocrystals in case of solid parahydrogen containing electrons and H6+ radical cations

“…22 Their isotopic analogs ͑H 6−n D n + ͑4 Ն n Ն 1͒͒, including H 5 D + , H 4 D 2 + , and H 2 D 4 + were also detected. 22 In these analogs, the H 2 + -core and side-on H 2 molecules present in H 6 + are replaced by D 2 or HD molecules. Singly D 2 -substituted H 4 D 2 + is denoted as "H 4 D 2 + " and its doubly HD-substituted counterpart is denoted as "HD-sub.…”