Electron attachment to halomethanes at high temperature: CH(2)Cl(2), CF(2)Cl(2), CH(3)Cl, and CF(3)Cl attachment rate constants up to 1100 K.
We have used a high-temperature flowing-afterglow Langmuir-probe apparatus to measure rate constants for electron attachment to halomethanes which attach electrons very inefficiently at room temperature, yielding Cl(-) ion product. We studied CH(2)Cl(2) (495-973 K), CF(2)Cl(2) (291-1105 K), and CF(3)Cl (524-1004 K) and include our recent measurement for CH(3)Cl (700-1100 K) in the discussion of the electron attachment results. The measured attachment rate constants show Arrhenius behavior in the temperature ranges examined, from which estimates of rate constants at 300 K may be made: CH(2)Cl(2) (1.8x10(-13) cm(3) s(-1)), CH(3)Cl (1.1x10(-17) cm(3) s(-1)), and CF(3)Cl (4.2x10(-14) cm(3) s(-1)), all of which are difficult to measure directly. In the case of CF(2)Cl(2), the room temperature rate constant was sufficiently large to be measured (1.6x10(-9) cm(3) s(-1)). The Arrhenius plots yield activation energies for the attachment reactions: 390+/-50 meV (CH(2)Cl(2)), 124+/-20 meV (CF(2)Cl(2)), 670+/-70 meV (CH(3)Cl), and 406+/-50 meV (CF(3)Cl). Comparisons are made with existing data where available. G3 calculations were carried out to obtain reaction energetics. They show that the parent anions of CH(2)Cl(2) CF(2)Cl(2), CH(3)Cl, and CF(3)Cl are stable, though CH(3)Cl(-) exists only as an electrostatically bound complex.
Miller
Thomas M
TM
Space Vehicles Directorate, Air Force Research Laboratory, 29 Randolph Road, Hanscom Air Force Base, Massachusetts 01731-3010, USA. thomas.miller@hanscom.af.mil
Friedman
Jeffrey F
JF
Schaffer
Linda C
LC
Viggiano
A A
AA