A complex excitation bands of RbCs are obtained near 640 nm in a very cold molecular beam using the resonance enhanced two photon ionization (RE2PI) method. Four progressions are observed in this region. From the high resolution analysis, they are identified four electronic states [$2^1π_1, 2^3π_0, 2^3π_1$, and $3 ^3Σ^{+}_1]$ . Although only $2^1π_1 - X ^1Σ^{+}_1$ is allowed transition, the other transitions [$2^3π_0- X^1Σ^{+}_1, 2^3π_1- X ^1Σ^{+}_1$, and $3 ^3Σ_^{+}_1- X ^1Σ^{+}_1$] are possible through the spin-orbit coupling with $^1Σ^{+}_1 and 2 ^{1}π_{1}$ state. We determined term values for $2 ^π_0, 2 ^3π_1, 2 ^1π_1$ states. For $3 ^3Σ^{+}_1$ state, determination of term values is impossible because of complete mixing with other states.
The A type doubling is also observed between $2 ^1π_1$ and $2 ^3π_0$ state, from the rotational line analysis. And we determined the spin-orbit coupling constant, A of $2 ^3π$ state in RbCs first time.
