MATRIX ISOLATION ELECTRON SPIN RESONANCE INVESTIGATION OF H2_2+^+, H4_4+^+, AND THEIR ISOTOPOMERS

Author Institution: Department of Chemistry, Furman University, Greenville, S.C. 29613Hydrogen cluster ions are of interest as reactants in astrophysical processes and as simple models for theoretical calculations. In this work, H$_4$$^+$ and its deuterated isotopomers were isolated in a neon matrix and investigated by electron spin resonance spectroscopy. The various isotopomers were formed by mixing H$_2$, D$_2$, and HD gases with neon and depositing the mixtures onto a copper rod cooled to 2.6 K. The matrices were then x-irradiated at 60 keV for 30 minutes. Electron spin resonance spectra were recorded for H$_4$$^+$, H$_3$D$^+$, H$_2$D$_2$$^+$, HD$_3$$^+$, and D$_4$$^+$ at temperatures ranging from 2.6 K to 9 K. These isotopomers could only be formed at 2.6 K, and were very sensitive to changes in temperature. Diatomic hydrogen ions (H$_2$$^+$ and HD$^+$) were also observed at 2.6 K at low sample gas concentrations. Experimental values for the hyperfine interactions were determined by fitting the observed hyperfine structure lines with those obtained from an exact diagonalization of the spin Hamiltonian

Electron spin resonance investigation of H\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e+\u3c/sup\u3e, HD\u3csup\u3e+\u3c/sup\u3e, and D\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e+\u3c/sup\u3e isolated in neon matrices at 2 K

Various isotopologues of nature\u27s simplest molecule, namely H(2)(+), HD(+), and D(2)(+), have been isolated in neon matrices at 2 K for the first time and studied by electron spin resonance (ESR). Over many years, hundreds of matrix isolation experiments employing a variety of deposition conditions and ion generation methods have been tried to trap the H(2)(+) cation radical in our laboratory. The molecule has been well characterized in the gas phase and by theoretical methods. The observed magnetic parameters for H(2)(+) in neon at 2 K are: g(-ˆ¥) -‰ˆ g(-Š¥) = 2.0022(1); A(iso)(H) = 881(7) MHz; and A(dip)(H) = 33(3) MHz. Reasonable agreement with gas phase values of the isotropic hyperfine interaction (A(iso)) is observed; however, the neon matrix dipolar hyperfine interaction (A(dip)) is noticeably below the gas phase value. The smaller matrix value of A(dip) is attributable to motional averaging of the H(2)(+) radical in the neon matrix trapping site--an occurrence that would prevent the full extent of the hyperfine anisotropy from being measured for a powder pattern type ESR sample