1. Department of Chemistry; University of Sheffield; Brook Hill Sheffield S3 7HF UK
2. University of California Berkeley; Berkeley CA 94720 USA
3. Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council; Rutherford Appleton Laboratory; Didcot Oxfordshire OX11 0QX UK
4. Department of Chemistry; Moscow Lomonosov State University; Russia