[1] Univ Toronto, Dept Phys, Toronto, ON M5S 1A7, Canada
[2] Univ New Brunswick, Dept Phys Sci, Ctr Laser Applicat & Mol Sci, St John, NB E2L 4L5, Canada
[3] Univ New Brunswick, Dept Phys, Ctr Laser Applicat & Mol Sci, Fredericton, NB E3B 5A3, Canada
[4] Univ Giessen, Inst Phys Chem, D-35392 Giessen, Germany