ABSTRACT
Table 474 shows the total scattering cross section in CH3Br and Figure 471 is a graphical presentationThe highlights of the cross section variation are
1 The cross section toward zero energy shows an increasing trend, common to most polar molecules
2 A small peak at 25 eV attributed to the formation of negative ions (Guerra et al, 1991)
3 A much larger peak at 10 eV also attributed to the attachment process
4 A monotonic decrease for energies >10 eV, up to 600 eV
TABLE 47.1 Selected Properties of Halogen-Substituted Methanes
Property CH3Br CH3Cl CH3F CH3I
z 44 26 18 62
αe (10−40 F m2) 618, 653, 671 525, 595 330 887 µ (D) 1820 1896 1858 1641 εa (eV) 011 εd (eV) 443 434 439 447 εi (eV) 10541 1122 1247 9538
Note:z = Number of electrons; αe = electronic polarizability; µ = dipole moment; εa = electron affinity; εd = dissociation energy; εi = ionization potential
TABLE 47.2 Vibrational Modes and Energies
Energy (meV)
Mode Designation CH3Br CD3Br
ν1 3685 2674 ν2 1618 1232 ν3 755 698 ν4 3790 2843 ν5 1790 1310 ν6 1183 882
Source:Adapted from LMSverdlov, MAKovner, and EPKrainov, Vibrational Spectra of Polyatomic Molecules, John Wiley & Sons, New York, NY, 1974, p 381
471 Selected References for Data 299 472 Total Scattering Cross Section 299 473 Total Ionization Cross Section 300 474 Positive Ion Appearance Potentials 301 475 Partial Ionization Cross Sections 301 476 Attachment Rate and Cross Section 301 477 Drift Velocity of Electrons 302 478 Mean Energy of Electrons 302 References 303
CH3I > CH3Br > CH3Cl
Table 475 shows the total ionization cross section in CH3Br (Vallance et al, 1997) and Figure 472 includes the graphical presentation
TABLE 47.3 Selected References for Data
Quantity Range: eV, (Td), (K) Reference
Qa 0-02 Braun et al. (2007) Qi 13-1000 Rejoub et al. (2002) QT 08-600 Kimura et al. (2001) Qa 0-10 Wilde et al (2000) Qi 105-220 Vallance et al. (1997) ka — Burns et al. (1996) QT 05-200 Krzysztofowicz and
Szmytkowski (1994) ka, W ≤1 Datskos et al. (1992) QT 05-8 Benitez et al. (1988) ka 0-12 Wang and Lee (1988) ka (293-500 K) Petrovic´ and Crompton (1987) ka (200-600 K) Alge et al. (1984) Qa <02, (300-1200 K) Spence and Schulz (1973) ka (03-6 Td) Christodoulides and
Christophorou (1971)
Note:ka = Attachment rate; W = drift velocity; Qa = attachment cross section; Qi = ionization; QT = total scattering; ε = mean energy Bold font denotes experimental study
TABLE 47.4 Total Scattering Cross Section in CH3Br
Energy (eV)
QT (10-20 m2)
Energy (eV)
QT (10-20 m2)
Energy (eV)
QT (10-20 m2)
08 518 65 404 22 346 10 448 70 410 25 325 12 431 75 427 30 300 14 415 80 423 40 257 16 294 85 421 50 232 18 383 90 422 60 211 20 381 95 427 70 200 22 384 10 429 80 182 25 387 11 421 90 177 28 371 12 417 100 163 31 365 13 406 120 154 34 356 14 398 150 138 37 356 15 390 200 117 40 349 16 387 250 109 45 372 17 377 300 91 50 374 18 373 400 82 55 380 19 367 500 69 60 383 20 352 600 60
Source:Adapted from Kimura, M et al, J. Chem. Phys, 115, 7442, 2001
TABLE 47.5 Ionization Cross Section in CH3Br
Energy (eV)
QT (10-20 m2)
Energy (eV)
QT (10-20 m2)
Energy (eV)
QT (10-20 m2)
12 083 82 722 153 620 16 143 86 720 156 613 20 279 90 714 160 605 23 399 94 706 164 600 27 490 97 697 167 594 31 529 101 694 171 588 34 572 105 690 175 580 38 607 108 684 179 576 42 639 112 676 182 576 45 665 116 668 186 576 49 685 119 665 190 574 53 700 123 663 193 567 57 709 127 658 197 559 60 718 130 649 201 551 64 722 134 639 204 546 68 725 138 632 208 542 71 728 142 627 212 540 75 728 145 625 215 538 79 725 149 624
Source:Courtesy of Professor P Harland (2006)
Bromomethane
Rejoub et al. (2002) Vallance et al. (1997)
Energy (eV) 10
Q i (1
m 2 )
See Table 476
Rejoub et al (2002) have measured the partial ionization cross sections for the fragments CHnBr+, CHn+, Br+, and H+, as shown in Table 477 and Figure 473
Pshenichnyuk et al (2006) observed peaks in negative ion formation at 00, 06, 68, and 90 eV in the ratio 3:9:08:04
Dissociative attachment of electrons below ~1 eV energy occurs via reaction
e + CH3Br → CH3 + Br− (471)
The electron affinity (εa) of bromine is 337 eV and the dissociation energy (D) is 3078 eV so that the negative ion state has the energy (D-εa) −0292 eV This is below the ground-state vibrational level of CH3-Br (Datskos et al, 1992)Christophorou and Hadjiantoniou (2006) quote that the electron affinity is >−046 eV
The thermal attachment rate coefficient as a function of E/N (reduced electric field, Td) is shown in Table 479 Datskos et al (1992) have measured the attachment rates as a function of temperature as shown in Table 4710 and Figure 474
Table 478 also shows the attachment rate coefficient at higher temperatures measured by several methods
The swarm-derived attachment cross section in CH3Br as a function of electron energy and temperature is shown in Figure 475 (Tsuda et al, 1964)
TABLE 47.7 Selected Partial Ionization Cross Sections
Energy (eV)
Qi (CHnBr+) (10−20 m2)
Qi (CHn+) (10−20 m2)
Q (Total) (10−20 m2)
13 0382 0382 14 0729 0729 16 135 0158 1508 18 182 0415 2235 20 216 0684 2844 225 257 0958 3608 25 301 125 4427 30 324 166 5249 35 343 202 6007 40 353 229 6581 50 359 249 7091 60 358 260 7411 80 357 269 7679 100 352 262 7571 125 327 254 7145 150 310 238 6699 200 282 207 5850 300 236 172 4797 400 202 151 4085 500 177 129 3531 600 158 114 3117 800 122 0876 2407 1000 109 0799 2149
Source:Adapted from Rejoub, R, BGLindsay, and RFStebbings, J. Chem. Phys, 117, 6450, 2002
TABLE 47.6 Appearance Potentials of Positive Ions of Selected Species
Appearance Potential (eV)
Process Photoionizationa Electron Ionizationb
CH3+ + Br− <102 107 CH3Br+ 1075 105
CH3+ + Br 1275 130 CH2Br+ + H 1375 CHBr+ + H2 1525 CH2 + HBr 1575 CH3 + Br+1825 147 CBr+ + H2 + H 2075 CH + HBr + H+2425
a Olney et al (1997) b Tsuda et al (1964)
10 100 Energy (eV)
1000 10 100 1000
10 100 100010 100 1000
6 Total Total
CHnBr+
Br+
H+
CHn+Bromomethane
Total Total
CH3Br
Q i (1
m 2 )
See Table 4711
See Table 4712
TABLE 47.10 Attachment Rate as a Function of Temperature
Temperature Rate
(10−18 m3/s) Reference
293 60 Burns et al (1996) 615 830 777 9500 300 110 Datskos et al (1992) 400 170 500 710 600 1600 700 3300 293 67 Petrovic´ and Crompton (1987) 445 180 499 440 300 60 Alge et al (1984) 452 230 585 2500
TABLE 47.9 Selected Attachment Rates as a Function of Temperature and E/N
E/N (Td) Ka (10−17 m3/s)
T =300K T =400K
0062 115 175 0124 135 182 0248 191 177 0528 281 154 1087 291 115 1240 277 107 1550 253 92 1860 235 82 2170 221 73 2480 205 66 3100 182 58 3730 168 52 4660 152 46
TABLE 47.8 Thermal Attachment Rates in CH3Br
Temperature (K) Method
Attachment Rate
(10-18 m3/s) Reference
293 FA/ECR 60 Burns et al (1996) 300 Swarm 108 Datskos et al (1992) ~298 Swarm 60 Wang and Lee (1988) 293 CM 67 Petrovic´ and Crompton (1987) 300 FA/LP 60 Alge et al (1984) 298 MC 70 Bansal and Fessenden (1972)
Source:Adapted from Christophorou, LGand DHadjiantoniou, J. Chem. Phys. Lett, 419, 405, 2006
Note:CM = Cavalleri method; FA/ECR = flowing afterglow/electron cyclotron resonance; MC = microwave conductivityRecommended value = 65 × 10−18 m3/s
0.0 0.2 0.4 Energy (eV)
0.6 0.8 1.0
Q a (1
m 2 ) 300 K
300 K
Attachment X-section
400 K
400 K
500 K
500 K 600 K
600 K
700 K
700 K
0.01 E/N (Td)
0.1 1 10
Ra te
(1 0-
)
3 700 K
Selected Attachment Rates as a Function of Temperature and E/N
E/N (Td) Ka (10−17 m3/s)
T =300K T =400K 5280 142 44 6210 133 42
Source:Adapted from Datskos, PG, LG Christophorou, and JGCarter, J. Chem. Phys, 97, 9031, 1992
Selected D2 + CH3 Function of Temperature and E/N
E/N (Td)
Drift Velocity (104 m/s)
T =300K T =500K T =700K
0062 0185 0132 0108
0124 0257 0210 0181
0248 0299 0277 0261
0528 0363 0359 0358
1087 0462 0462 0470
2480 0692 0707 0728
5280 1142 1177 1205
Source:Adapted from Datskos, PG, LGChristophorou, and J G Carter, J. Chem. Phys, 97, 9031, 1992
Note:See Figure 476 for graphical presentation
TABLE 47.12 Selected Mean Energy for (N2 + CH3Br) as a Function of Temperature and E/N
E/N (Td)
Mean Energy (eV)
T =300K T =500K T =700K
0062 0046 0070 0092
0124 0065 0085 0104
0248 0111 0125 0139
0528 0204 0217 0221
1087 0374 0378 0388
2170 0601 0601 0601
4660 0812 0812 0812
5280 0839 0839 0839
6210 0872 0872 0872
Source:Adapted from Datskos, PG, LGChristophorou, and J G Carter, J. Chem. Phys, 97, 9031, 1992
Note:See Figure 477 for graphical presentation
0.01 0.1 1
300 K
Drift velocity (CH3Br)
400 K 500 K 600 K 700 K
E/N (Td) 10
1.5
0.5
W (1
04 m
0.01 0.1 1
300 K
Bromomethane (CH3Br)
400 K 500 K 600 K 700 K
E/N (Td) 10
0.1
0.01
M ea
n en
er gy
(e V)
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