$\sigma 1s < \sigma^* 1s < \sigma 2s < \sigma^* 2s < \sigma 2p_z < \left( \pi 2p_x = \pi 2p_y \right) < \left( \pi^* 2p_x = \pi^* 2p_y \right) < \sigma^* 2p_z$

$\sigma 1s < \sigma^* 1s < \sigma 2s < \sigma^* 2s < \sigma 2p_z < \sigma^* 2p_z < \left( \pi 2p_x = \pi 2p_y \right) < \left( \pi^* 2p_x = \pi^* 2p_y \right)$

$\sigma 1s < \sigma^* 1s < \sigma 2s < \sigma^* 2s < (\pi 2p_x = \pi 2p_y) < \left( \pi^* 2p_x = \pi^* 2p_y \right) < \sigma 2p_z < \sigma^* 2p_z$