哈龙1301分子在外电场中的光谱特征和解离特性

Study on Dissociation Properties and Spectra of Halon 1301 in External Electric Field

哈龙1301(三氟溴甲烷)在太阳光辐射下解离生成破坏臭氧的溴自由基,严重破坏大气臭氧层,采用有效的措施对哈龙1301排放前进行降解很有必要。利用密度泛函理论(DFT)在B3LYP/6～311G++(d,p)水平上研究了外电场(0～0.03 a.u.)作用下哈龙1301分子的解离特性和光谱特征,包括总能量,键长,电偶极矩,LUMO-HOMO能隙,红外光谱以及解离势能面等。计算结果表明,在C——Br键连线Z方向上,外电场从0逐渐增加到0.03 a.u.时,分子体系能量逐渐减小,偶极矩在刚开始表现为减小然后单调增大,HOMO-LUMO能隙E_G呈现单调递减的趋势,C——Br键键长逐渐增大,C——F键键长逐渐减小。外电场对CF_3Br分子不同振动模式的红外光谱影响不同。在外电场作用逐渐增强下,解离特性表现为:CF_3Br分子的C——Br键方向扫描得到的势能曲线的束缚状态逐渐被消除,势垒逐渐变小最后消失。计算发现强度为0.03 a.u.的外电场足够使得CF_3Br分子发生C——Br键断裂而降解,该结果为保护环境而对哈龙进行电场降解提供重要参考依据。

Halon-1301（CF3Br） can make Br radicals with UV radiation,which poses a great threat to the ozone layer in the atmosphere.Necessary methods should be taken for the degradation of the exhausts of Halon-1301.In this paper,density functional（DFT） theory at B3LYP/6-311G＋ ＋（d,p） level are employed for the study of dissociation properties and spectra of Halon-1301 in external electric field,including bond length,total energy,HOMO-LUMO energy gap,infrared spectra and dissociation potential energy surface（PES）.The obtained results show that,with gradually increasing the external field from 0 to0.03 a.u.along the molecular axis Z（C—Br bond direction）,the total energy decreases,while the dipole moment decreases at the beginning and then increases.With the climbing of the field,HOMOLUMO energy gap increases,and C—Br bond length increases while C—F bond length decreases.The variations of vibrational frequency and intensity of molecular IR spectra in external electric field are also investigated.Further studies show that with increasing the external electric field from 0 to 0.03 a.u.,the dissociation PES along C—Br bond becomes unbound with disappearing of the barrier for the dissociation.The external electric field of 0.03 a.u.is sufficient to induce the degradation of CF_3 Br with C—Br bond breaking.Such results provide an important reference for the degradation of Halons via the external electric field.