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Lithium imide ͑Li 2 NH͒ has been considered as a promising medium for hydrogen storage with the following reaction: LiNH 2 + LiH↔ Li 2 NH+ H 2 . All possible phases involved in the reaction need to be fully characterized in order to understand the right pathway connecting the two end compounds LiNH 2 and Li 2 NH and to further improve its reaction condition to meet the requirements of practical applications. We study from first-principles calculations the possible intermediate compounds Li 2−x NH 1+x between Li 2 NH and LiNH 2 . Based on the energetics results, possible intermediate phases are identified for 0 Ͻ x Յ 1 / 4. On the other hand, the intermediate phases are not thermodynamically favorable for 3 / 4 Յ x Ͻ 1 with respect to phase separation into Li 2 NH and LiNH 2 . The NH and NH 2 anions coexist in the intermediate compounds, but the electronic states derived from these two units are well separated in energy. The band gap of the intermediate compounds is also smaller than that of both Li 2 NH and LiNH 2 . These signatures from the electronic structure will provide useful guidelines for experimental efforts to search for the intermediate phases.

The predissociation dynamics of B Rydberg state of methyl iodide has been studied with femtosecond two-color pump-probe time-of-flight spectra at pump pulse of 400nm and probe pulse 800 nm. The dominant product channels are the CH3I+ and CH3+ formation. The time-dependent signals for CH3I+ and CH3+ ions are obtained. Both of the signal curves can be fitted by biexponential decays with time constants of O 1 and O 2, O 1 was assigned to the lifetimes of high Rydberg states, which can be accessed by absorbing three 400 nm pump pulses and O 2 reflects the dynamics of B Rydberg state, which is accessed with two pump pulses. The lifetime of B Rydberg state is determined to be about 1.57 ps, which is incredibly consistent with the previous studies. The results were interpreted as a multiphoton dissociative ionization processes.

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