All the energies are negative because it is a bound system. I start up here with n equals one.

所有能量级都是负数，因为它是一个束缚系统,在这里我从n等于1讲起。

麻省理工公开课 - 固态化学导论课程节选

Absorption is just the opposite of emission, so instead of starting at a high energy level and dropping down, when we absorb light we start low and we absorb energy to bring ourselves up to an n final that's higher.

吸收就是发射的逆过程,与从一个高能量到低能量不同，当吸收光时，我们从低能量开始,吸收能量到一个更高的能量。

麻省理工公开课 - 化学原理课程节选