1. Chemistry, School of Science, University of Waikato , Private Bag 3105 , Hamilton , New Zealand
2. Current address: Institute of Environmental Science and Research (ESR) , PO Box 50348 , Wellington 5240 , New Zealand
3. School of Chemical Sciences, University of Auckland , Auckland , New Zealand
4. Current address: Research School of Chemistry, Australian National University , Canberra, ACT2600 , Australia
5. School of Fundamental Sciences, Massey University , Private Bag 11222 , Palmerston North 4410 , New Zealand