Al3+, Ca2+, Mg2+, and Li+ in aqueous solution: calculated first-shell anharmonic OH vibrations at 300 K.
The anharmonic OH stretching vibrational frequencies, ν(OH), for the first-shell water molecules around the Li(+), Ca(2+), Mg(2+), and Al(3+) ions in dilute aqueous solutions have been calculated based on classical molecular dynamics (MD) simulations and quantum-mechanical (QM) calculations. For Li(+)(aq), Ca(2+)(aq), Mg(2+)(aq), and Al(3+)(aq), our calculated IR frequency shifts, Δν(OH), with respect to the gas-phase water frequency, are about -300, -350, -450, and -750 cm(-1), compared to -290, -290, -420, and -830 cm(-1) from experimental infrared (IR) studies. The agreement is thus quite good, except for the order between Li(+) and Ca(2+). Given that the polarizing field from the Ca(2+) ion ought to be larger than that from Li(+)(aq), our calculated result seems reasonable. Also the absolute OH frequencies agree well with experiment. The method we used is a sequential four-step procedure: QM(electronic) to make a force field+MD simulation+QM(electronic) for point-charge-embedded M(n+) (H(2)O)(y) (second shell) (H(2)O)(z) (third shell) clusters+QM(vibrational) to yield the OH spectrum. The many-body Ca(2+)-water force-field presented in this paper is new. IR intensity-weighting of the density-of-states frequency distributions was carried out by means of the squared dipole moment derivatives.
Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, P.O. Box 162, 1000 Skopje, Republic of Macedonia.
Ljupčo
L
Pejov
Daniel
D
Spångberg
Kersti
K
Hermansson
D000465:Algorithms; D000535:Aluminum / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002412:Cations / Q000737:chemistry*; D006878:Hydroxides / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012996:Solutions / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013696:Temperature; D014732:Vibration; D014867:Water / Q000737:chemistry*
D002412:Cations; D006878:Hydroxides; D012996:Solutions; D014867:Water; D008094:Lithium; D000535:Aluminum; D008274:Magnesium; D002118:Calcium