Bromoacetaldehyde (BrCH₂CHO) is a major stable brominated organic intermediate of the bromine–ethylene addition reaction during the arctic bromine explosion events. Similar to acetaldehyde, which has been recently identified as a source of organic acids in the troposphere, it may be subjected to photo-tautomerization initially forming brominated vinyl compounds. In this study, we investigate the unimolecular reactions of BrCH₂CHO under both photolytic and thermal conditions using high-level quantum chemical calculations and Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation analysis. The unimolecular decomposition of BrCH₂CHO takes place through 14 dissociation and isomerization channels along a potential energy surface involving eight wells. Under the assumption of singlet ground-state potential energy surface-dominated photodynamics, the primary photodissociation yields of BrCH₂CHO are investigated under both collision-free and collision energy transfer conditions. At atmospheric pressure and under tropospheric actinic flux conditions at ground level, depending on the assumed collisional energy transfer parameter, 150 cm^–1 < ⟨ΔE_down⟩ < 450 cm^–1, 78–33% of BrCH₂CHO undergoes direct photodissociation instead of collisional deactivation at an excitation wavelength of 320 nm. This is significantly higher than the 14% reported for acetaldehyde, hence indicating a strong effect of bromine substitution on the product photolysis yield that is related to additional favorable Br and HBr forming dissociation channels. In contrast to the overall photodissociation quantum yield, the relative branching fractions of the photodissociation products are less dependent on the collisional energy transfer parameter. For a representative value of ⟨ΔE_down⟩ = 300 cm^–1 and an excitation wavelength of 320 nm, with 27% for C–C bond fission, 11% for C–Br bond fission, 7% for HBr elimination, and only below 2% each for a consecutive O–Br fission reaction and the photo-tautomerization channel yielding brominated vinyl alcohol, the photodissociation is markedly different from the acetaldehyde case. Finally, as brominated halogenated compounds are of interest for flame inhibition purposes, thermal multichannel unimolecular rate constants were calculated for temperatures in the range from 500 to 2000 K. At a temperature of 2000 K and ambient pressure, the two main reaction channels are the C–Br and C–C bond fissions, contributing 35 and 43% to the total reaction flux, respectively.

中文翻译：

---

溴乙醛光解和热单分子分解的 Ab Initio 和 RRKM/主方程分析

溴乙醛 (BrCH ₂ CHO) 是北极溴爆炸事件期间溴-乙烯加成反应的主要稳定溴化有机中间体。与最近被确定为对流层中有机酸来源的乙醛类似，它可以进行光互变异构化，最初形成溴化乙烯基化合物。在本研究中，我们使用高级量子化学计算和 Rice-Ramsperger-Kassel-Marcus (RRKM)/主方程分析研究了 BrCH ₂ CHO 在光解和热条件下的单分子反应。BrCH ₂的单分子分解CHO 通过 14 个离解和异构化通道沿着涉及 8 个孔的势能表面发生。在单线态基态势能表面主导光动力学的假设下，在无碰撞和碰撞能量转移条件下研究了 BrCH ₂ CHO的初级光解产率。在大气压和地面对流层光化通量条件下，取决于假设的碰撞能量转移参数，150 cm ^–1 < ⟨Δ E _down ⟩ < 450 cm ^–1，BrCH _{2 的}78–33%CHO 在 320 nm 的激发波长下经历直接光解而不是碰撞失活。这明显高于乙醛报道的 14%，因此表明溴取代对产物光解产率的强烈影响，这与额外的有利 Br 和 HBr 形成解离通道有关。与整体光解量子产率相比，光解产物的相对支化分数不太依赖于碰撞能量转移参数。对于代表值 ⟨Δ E _down ⟩ = 300 cm ^–1激发波长为 320 nm，其中 C-C 键裂变为 27%，C-Br 键裂变为 11%，HBr 消除为 7%，连续 O-Br 裂变反应和照片各仅低于 2% -互变异构通道产生溴化乙烯醇，光解与乙醛情况明显不同。最后，由于溴化卤化化合物对于抑制火焰的目的很重要，因此计算了 500 到 2000 K 温度范围内的热多通道单分子速率常数。在 2000 K 和环境压力下，两个主要反应通道是 C –Br 和 C–C 键裂变，分别占总反应通量的 35% 和 43%。