[1] UCL, Dept Phys & Astron, London WC1E 6BT, England
[2] Nizhnii Novgorod State Univ, Dept Math, Nizhnii Novgorod, Russia
[3] Univ Waterloo, Dept Chem, Waterloo, ON N2L 3G1, Canada
[4] Univ Waterloo, Dept Phys, Waterloo, ON N2L 3G1, Canada
[5] Natl Opt Astron Observ, Tucson, AZ 85732 USA