1. Department of Physics and MathematicsUniversity of Hull Cottingham Rd HU6 7RX Hull UK
2. Physics DepartmentCollege of ScienceUniversity of Baghdad Baghdad 10071 Iraq
3. School of Science and TechnologyNottingham Trent University Clifton Lane NG11 8NS Nottingham UK
4. Department of Chemistry and BiochemistryUniversity of Hull Cottingham Rd HU6 7RX Hull UK