We describe recent experiments in which mass spectrometry and laser spectroscopy are combined to characterize Li+–H2, Na+–H2, B+–H2 and Al+–H2 complexes in the gas-phase. The infrared spectra, which feature full resolution of rotational sub-structures, are recorded by monitoring M+ photofragments as the infrared wavelength is scanned. The spectra deliver detailed information on the way, in which a hydrogen molecule is attached to a metal cation including the intermolecular separation, the force constant for the intermolecular bond and the H–H stretching frequency. The complexes all possess T-shaped equilibrium geometries and display a clear correlation between the length and force constant of the intermolecular bond and the dissociation energy. In contrast, the data do not support any straight forward correlation between the frequency shift for the H–H stretch mode and the dissociation energy.
KemperP.R.WeisP.BowersM.T., “Cr+(H2)n clusters: Asymmetric bonding from a symmetric ion”, Int. J. Mass Spectrom. Ion Processes160, 17 (1997). doi: 10.1016/S0168-1176(96)04493-X
2.
ArmentroutP.B., “Periodic trends in the reactions of atomic ions with molecular hydrogen”, Int. Rev. Phys. Chem.9, 115 (1990). doi: 10.1080/01442359009353244
3.
OkumuraM.YehL.I.LeeY.T., “Infrared spectroscopy of the cluster ions H3+(H2)n”, J. Chem. Phys.88, 79 (1988). doi: 10.1063/1.454488
4.
LisyJ.M., “Spectroscopy and structure of solvated alkali-metal ions”, Int. Rev. Phys. Chem.16, 267 (1997). doi: 10.1080/014423597230208
5.
DuncanM.A., “Infrared spectroscopy to probe structure and dynamics in metal ion–molecule complexes”, Int. Rev. Phys. Chem.22, 407 (2003). doi: 10.1080/0144235031000095201
6.
MacAleeseL.MâitreP., “Infrared spectroscopy of organometallic ions in the gas phase: From model to real world complexes”, Mass Spectrom. Rev.26, 583 (2007). doi: 10.1002/mas.20138
7.
PolferN.C.OomensJ., “Vibrational spectroscopy of bare and solvated ionic complexes of biological relevance”, Mass Spectrom. Rev.28, 468 (2008). doi: 10.1002/mas.20215
8.
EmmeluthC.PoadB.L.J.ThompsonC.D.WeddleG.H.BieskeE.J., “Infrared spectra of the Li+–(H2)n (n = 1–3) cation complexes”, J. Chem. Phys.126, 204309 (2007). doi: 10.1063/1.2738464
9.
PoadB.L.J.WearneP.J.BieskeE.J.BuchachenkoA. A.BennettD.I.G.KłosJ.AlexanderM.H., “The Na+–H2 cation complex: Rotationally resolved infrared spectrum, potential energy surface, and rovibrational calculations”, J. Chem. Phys.129, 184306 (2008). doi: 10.1063/1.3005785
10.
DryzaV.PoadB.L.J.BieskeE.J., “Attachment of molecular hydrogen to an isolated boron cation: An infrared and ab initio study”, J. Am. Chem. Soc.130, 12986 (2008). doi: 10.1021/ja8018302
11.
EmmeluthC.PoadB.L.J.ThompsonC.D.WeddleG.H.BieskeE.J.BuchachenkoA.A.GrinevT.A.KłosJ., “The Al+–H2 cation complex: Infrared spectrum, potential energy surface and rovibrational calculations”, J. Chem. Phys.127, 164310 (2007). doi: 10.1063/1.2778422
12.
FelderhoffM.WeidenthalerC.von HelmoltR.EberleU., “Hydrogen storage: The remaining scientific and technological challenges”, Phys. Chem. Chem. Phys.9, 2643 (2007). doi: 10.1039/b701563c
13.
van den BergA.W.C.AreánC. Otero, “Materials for hydrogen storage: Current research trends and perspectives”, Chem. Commun.668 (2008). doi: 10.1039/b712576n
14.
BauschlicherC.W., “The ground and low-lying excited-states of MgH2+”, Chem. Phys. Lett.201, 11 (1993). doi: 10.1016/0009-2614(93)85025-J
15.
LochanR.C.Head-GordonM., “Computational studies of molecular hydrogen binding affinities: The role of dispersion forces, electrostatics, and orbital interactions”, Phys. Chem. Chem. Phys.8, 1357 (2006). doi: 10.1039/b515409j
16.
DryzaV.PoadB. L.BieskeE. J., “Infrared Spectra of Mass-Selected Mg+–H2 and Mg+–D2 Complexes”, J. Phys. Chem. A113, 199 (2009). doi: 10.1021/jp808807r
17.
KraemerW.P.SpirkoV., “Bound and low-lying quasi-bound rotation-vibration levels of the ground electronic state of LiH2+”, Chem. Phys.330, 190 (2006). doi: 10.1016/j.chemphys.2006.08.011
18.
PageA.J.von Nagy-FelsobukiE.I., “Ab Initio rovibrational spectrum of the NaH2+ ion–quadrupole complex”, Theoret. Chem. Acc.122, 87 (2009). doi: 10.1007/s00214-008-0487-7
19.
KemperP.R.BushnellJ.E.WeisP.BowersM.T., “Cluster-assisted thermal energy activation of the H–H sigma bond in H2 by ground state B+(1S0) ions: Overcoming a 77 kcal/mol barrier”, J. Am. Chem. Soc.120, 7577 (1998). doi: 10.1021/ja9739751
20.
WildD.A.WilsonR.L.LohZ.M.BieskeE.J., “The infrared spectrum of the F−–H2 anion complex”, Chem. Phys. Lett.393, 517 (2004). doi: 10.1016/j.cplett.2004.06.078
21.
WildD.A.WeiserP.S.BieskeE.J.ZehnackerA., “The 35Cl−–H2 and 35Cl−–D2 anion complexes: Infrared spectra and radial intermolecular potentials”, J. Chem. Phys.115, 824 (2001). doi: 10.1063/1.1378039
22.
WildD.A.LohZ.M.WilsonR.L.BieskeE.J., “Br−–H2 and I−–H2 anion complexes: Infrared spectra and radial intermolecular potential energy curves”, J. Chem. Phys.117, 3256 (2002). doi: 10.1063/1.1486435
23.
VitilloJ.G.DaminA.ZecchinaA.RicchiardiG., “Theoretical characterization of dihydrogen adducts with alkaline cations”, J. Chem. Phys.122, 114311/1 (2005). doi: 10.1063/1.1869418
24.
OlkhovR.V.NizkorodovS.A.DopferO., “Hindered rotation in ion–neutral molecular complexes: The ν1 vibration of H2–HCO+ and D2–DCO+”, J. Chem. Phys.107, 8229 (1997). doi: 10.1063/1.475027
