 When xenon atoms are at their ground energy state , they repel each other and will not form a bond . When xenon atoms becomes <unk> , however , they can form an excimer ( excited dimer ) until the electrons return to the ground state . This entity is formed because the xenon atom tends to fill its outermost electronic shell , and can briefly do this by adding an electron from a neighboring xenon atom . The typical lifetime of a xenon excimer is 1 – 5 <unk> , and the decay releases photons with <unk> of about 150 and 173 nm . Xenon can also form <unk> with other elements , such as the <unk> <unk> , chlorine and fluorine . 
