"A sweet temper" is a figurative expression, but "sweet coffee" is not. "甜蜜的性情"是个比喻的说法,而"甜咖啡"则不是。
Its absorption by a molecule causes all sorts of subtle changes in the vibrational or rotational energy of the molecule. 一个分子能吸收红外光引起分子中振动能量和旋转能量的各种各样的微小变化。