In steady state, both the capacitors are at the same potential, i.e., \(\frac{ Q _1}{ C _1}=\frac{ Q _2}{ C _2}\) or \(\frac{ Q _1}{ C }=\frac{ Q _2}{2 C }\) or \(Q _2=2 Q _1\)
Also \(Q _1+ Q _2= Q\)
\(\therefore Q _1=\frac{ Q }{3}, Q _2=\frac{2 Q }{3}\)