The transition from state n = 4 to n = 3 in a He+ ion result in ultraviolet radiation. Infrared radiation will be obtained in the transition from
n=8→n=6
In case of H-spectrum UV spectrum appears from n1=1, to n2=2,3....
Here in case of He+ spectrum UV spectrum is from n1 to n2=4.
¯νUV=RZ2(132−142)R×4(132−142)
In case of H-spectrum IR appears from n1=3, n2=4,5....
¯νIR for H+2=R×12(132−142) .....(i)
¯νIR for He+=R×4(1n21−1n22)=R(4n21−4n22) .....(ii)
Comparing the coefficient of equation (i) and (ii), we get
4n21=19;n1=6
4n21=116;n2=8
Thus, transition for He+ in IR is n1→6 to n2→8.
Note: IR region starts with n1=3.