Chen L, Kutsuna S, Tokuhashi K, Sekiya A, Tamai R, Hibino Y
National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan.
J Phys Chem A. 2005 Jun 2;109(21):4766-71. doi: 10.1021/jp050491f.
The atmospheric chemistry of (CF3)2CHOCH3, a possible HCFC/HFC alternative, was studied using a smog chamber/FT-IR technique. OH radicals were prepared by the photolysis of ozone in a 200-Torr H2O/O3/O2 gas mixture held in an 11.5-dm3 temperature-controlled chamber. The rate constant, k1, for the reaction of (CF3)2CHOCH3 with OH radicals was determined to be (1.40 +/- 0.28) x 10(-12) exp[(-550 +/- 60)/T] cm3 molecule(-1) s(-1) by means of a relative rate method at 253-328 K. The value of k1 at 298 K was (2.25 +/- 0.04) x 10(-13) cm3 molecule(-1) s(-1). The random errors are reported with +/-2 standard deviations, and potential systematic errors of 15% could increase k(1). In considering OH-radical reactions, we estimated the tropospheric lifetime of (CF3)2CHOCH3 to be 2.0 months using the rate constant at 288 K. The degradation mechanism of (CF3)2CHOCH3 initiated by OH radicals was also investigated using FT-IR spectroscopy at 298 K. Products (CF3)2CHOC(O)H, CF3C(OH)2CF3, CF3C(O)OCH3, and COF(2) were identified and quantified. The branching ratio, k1a/k1b, was estimated to be 2.1:1 for reactions (CF3)2CHOCH3 + OH --> (CF3)2CHOCH2*+ H2O (k1a) and (CF3)2CHOCH3 + OH --> (CF3)2C*OCH3 + H2O (k1b).
采用烟雾箱/傅里叶变换红外光谱技术研究了一种可能的氢氯氟烃/氢氟烃替代品（CF3）2CHOCH3的大气化学性质。在一个11.5立方分米的温度控制箱中，通过在200托的H2O/O3/O2气体混合物中光解臭氧来制备羟基自由基。在253 - 328K温度范围内，采用相对速率法测定了（CF3）2CHOCH3与羟基自由基反应的速率常数k1为（1.40±0.28）×10（-12）exp[（-550±60）/T]立方厘米·分子（-1）·秒（-1）。298K时k1的值为（2.25±0.04）×10（-13）立方厘米·分子（-1）·秒（-1）。随机误差以±2标准偏差报告，15%的潜在系统误差可能会使k1增大。在考虑羟基自由基反应时，我们使用288K时的速率常数估计（CF3）2CHOCH3在对流层中的寿命为2.0个月。还在298K下使用傅里叶变换红外光谱研究了由羟基自由基引发的（CF3）2CHOCH3的降解机理。鉴定并定量了产物（CF3）2CHOC（O）H、CF3C（OH）2CF3、CF3C（O）OCH3和COF2。对于反应（CF3）2CHOCH3 + OH→（CF3）2CHOCH2* + H2O（k1a）和（CF3）2CHOCH3 + OH→（CF3）2C*OCH3 + H2O（k1b），分支比k1a/k1b估计为2.1:1。
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