In an ordianary atom, as a first approximation, the motion of the nucleus can be ignored. In a positronium atom a positronreplaces the proton of hydrogen atom. The electron and positron masses are equal and , therefore , the motion of the positron cannot be ignored. One must consider the motion of both electron and positron about their center of mass. A detailed analyasis shows that formulae of Bohr's model apply to positronium atom provided that we replace `m_(e)` by what is known reduced mass is `m_(e)//2`.
When system de-excites from its first excited state to ground state, the wavelngth of radiation is

Options

A. `1217 Å`
B. `2431 Å`
C. `608 Å`
D. none of these

Answer

B

Explanation

`(1)/(lambda) = ( R)/(2) ((1)/(1^(2)) - (1)/(2^(2)))`
`implies lambda = (8)/(3 R) = (8)/(3 xx 1.097 xx 10^(7)) = 2431 Å`