[1] Univ British Columbia, Dept Chem, Vancouver, BC, Canada
[2] Univ British Columbia, Dept Phys & Astron, Vancouver, BC V5Z 1M9, Canada
[3] Tech Univ Munich, Phys Dept E20, D-85748 Garching, Germany
[4] Western Washington Univ, Dept Phys & Astron, Bellingham, WA 98225 USA