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用从头算方法在MP2/6-31+G(d)水平下研究了尿素和甲醛反应机理,在从头算给出的信息基础上,用变分过渡态理论加小曲率隧道效应计算了(200~3000)K温度范围内尿素和甲醛反应的速率常数。脲与甲醛的反应是较简单的加成反应,反应的基元过程主要是氮氢键的断裂和氧氢键的生成。在MP2/6-31+G(d)理论水平下,反应的势垒高度为32.83kcal·mol-1。计算的速率常数展示出较强的非Arrhenius行为,速-温关系3参数公式拟合为:k (T )=(3.32×10(-43) )T (8.32)exp( -9027.8 / T) /(cm 3 ·molecule (-1) ·s( -1) )。
The ab initio method was used to study the reaction mechanism between urea and formaldehyde at the level of MP2 / 6-31 + G (d). Based on the ab initio calculations and using the theory of variational transition states and the small curvature tunneling effect, (200 ~ 3000) K The rate constants of urea and formaldehyde reaction in the temperature range. The reaction of urea with formaldehyde is a simple addition reaction. The basic process of reaction is the cleavage of nitrogen-hydrogen bonds and the formation of oxygen-hydrogen bonds. Under MP2 / 6-31 + G (d) theoretical level, the barrier height of the reaction is 32.83 kcal · mol-1. The calculated rate constants show a strong non-Arrhenius behavior. The fitting of the three parameters of speed-temperature relationship is: k (T) = (3.32 × 10 (-43)) T (8.32) exp (-9027.8 / T) / (cm 3 · molecule (-1) · s (-1)).