中文摘要：

本文采用全相对论量子力学计算了H2 X （X=O, S, Se, Te）分子的双光子过程,并考虑相对论效应对双光子过程的影响。结果表明,各个不可约表示对称态下激发能有着明显的差异,它反应了双光子吸收过程中选择能级的特点。同时,采用非相对论的对称匹配簇/组态相互作用方法（SAC-CI）计算其分子的单光子激发,并与之比较。双光子跃迁概率要比单光子跃迁概率小2-5个数量级；同一主族,随着原子序数的增加,相对论效应对分子体系的激发能量、跃迁概率、振子强度的大小都有显著地影响；除此之外,每个分子遵守分子对称群的选择原则。本文中,分子H2X （X=O, S, Se, Te）的个别不可约表示对称态的跃迁矩分量和振子强度远远大于其他对称态下的跃迁矩分量和振子强度,甚至大于单光子激发。这不仅与分子的对称性有一定的关系,而且应该是选择双光子跃迁能级的重要依据。

英文摘要：

The present work is mainly to study two-photon process in H2X （X =O, S, Se, Te） by using the full relativistic theory. For comparison, we also study the single-photon process by SAC-CI method. The transition probability of two-photon excitation is 10？2-10？5 times of the single-photon process; the relativistic effects become more and more obvious with the increase of atomic number. In addition, every molecule observes the selection principles;dipole transition component and oscillator strength of individual symmetrical states are greater than those of other individual states. This is due to the symmetry of molecule and it should be an important basis for selecting transition energy.