1188
Durig et al.
magnitude K2r,. This is because Lir/yrl'z is of magnitude Kre, whereas Liss/ys is of magnitude K2rp,,but ( qr ) is of magnitude K , whereas ( q s 2 )is of magnitude 1.In practice both terms are typically around 0.005 A. Continuing this reasoning the next two terms in (5) would be of magnitude ~ ~ rperhaps ,, 100 times smaller still, and negligible compared to the precision of present measurements. Finally we show that the second and third terms in eq 5 correspond exactly to the second and third terms in eq 1.From eq 22 and 23 of Hoy et a1.,6 and the definition of Pir in their eq 20 and 21
giving the correction from rie to ria (or to riz in the ground vibrational state). The possible advantage of the formulation in eq 5 and 10 over that in eq 1and 2 is partly in the physical significance of the terms, and partly in convenience of calculation. Equation 5 brings out the fact that the Lir( QP) term arises from the average displacement in the totally symmetric coordinates due to cubic anharmonicity, whereas the Liss ( Qs2)term arises from the nonlinear nature of the transformation from interatomic distances to normal coordinates. It also appears to be a more direct relation between the quantities of interest than eq 1. Finally the calculation of the necessary L tensor elements is simple to program, and provides a convenient method of calculating vibrational averaging effects.
References and Notes (1)Research associate with Professor R. C. Lord, 1963-1964. (2)Y. Morino, J. Nakamura, and P. W. Moore, J. Chem. Phys., 36, 1050 (1962). (3) K. Kuchitsu, Bull. Chem. SOC. Jpn., 40,505 (1967). (4) K. Kuchitsu in "Molecular Structures and Vibrations", S.J. Cyvin, Ed., Elsevier, Amsterdam, 1972,Chapter 12. (5)Y. Morino, K. Kuchitsu, and T. Oka, J. Chem. fhys.. 36, 1108 (1962). (6)A. R. Hoy, I. M. Mills, and G. Strey, Mol. fhys., 24, 1265 (1972). (7) If the index s refers to a degenerate normal coordinate, the sum over s in eq 5 should be carried over each component of the degenerate mode. (8) T. Oka, J. Chem. Phys., 47,5410 (1967). (9)K = (m/1%9"~ is the Born-Oppenheimer expansion parameter; in terms of
where Axi, 4yi, and 4zi are the local Cartesian difference coordinates defined earlier, linearly related to the normal coordinates. Averaging (8) and (9) over a vibrational state proves the term by term equivalence of (1)and (5). Similarly it is clear that eq 2 can be written in the form
K,
E,,tlE,ib
N
EvlblEelectrN
K*,
and Ar/r
N K.
Microwave, Infrared, and Raman Studies of Several Isotopic Species of Vinyldifluoroborane J. R. Durig," laL. W. Hall,lb R. 0. Carter, C. J. Wurrey,lc V. F. Kalasinsky,ld and J. D. Odom Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208 (Received December 15, 1975) Publication costs assisted by the University of South Carolina
The microwave spectra of Fzl1Bl3CHCHz, FzllBCDCDz, F~~OBCDCDZ, Fzl1Bl3CDCDz, Fzl'BCDCHz, F211BCHCHD(2), F21°BCHCHD(2), F211BCDCHD(2), and FzlOBCDCHD(2) have been obtained and assigned in the range from 18 to 40 GHz. The 26 independent rotational constants along with the four previously determined ones were used to obtain a least-squares fit of the 13 structural parameters as follows: rC-C = 1.339 f 0.005, PB-C = 1.532 f 0.003, 7'B-F' = 1.331 f 0.002, rB-F = 1.331 f 0.002, rC,-H = 1.086 f 0.007, rCg-Ht = 1.087 zk 0.006, rCp-H = 1.087 f 0.006, LHCpC, = 122.31 f 0.56, LH'CsC, = 119.50 f 0.36, LF'BC = 121.72 f 0.48, LFBF' = 116.04 f 0.41, LCCB = 121.96 f 0.25, and LH,C,Cp = 117.84 f 0.69. Several of these structural parameters were obtained also by the r, method and they were found to be within the error limits of those obtained by the least-squares method. The most important parameter is the B-C distance which appears to be normal. The infrared (200-4000 cm-l) of gaseous and solid and Roman spectra (0-4000 cm-l) of gaseous, liquid, and solid FzBCDCD2 have been obtained and the spectra interpreted in detail. A normal coordinate calculation has been carried out using 17 diagonal force constants and four interaction constants to fit 36 fundamental frequencies. Slight coupling was found between the B-C and B-F stretching motions.
Introduction
The microwave, infrared, and Raman spectra of FzB(C2H3) have been reported in a previous study carried out in our laboratories.2 From this work a partial structure, dipole moThe Journal of Physical Chemistry, Vol. 80, No. 11, 1976
ment, and barrier to internal rotation of FzB(CzH3) were obtained. This earlier work was undertaken primarily because of our interest in the question of boron-carbon T bonding in the vinylboranes. The determination of the structure of FzB(CzH3) is of particular interest since our l3C NMR study3
Spectra of Vinyldifluoroborane of the vinylboranes found B-C K conjugation to occur to the greatest extent in the monovinylhaloboranes. A more detailed structural determination should provide a means of assessing if there are any dramatic effects due to potential fluorineboron prr-prr back-bonding. To provide such structural information a microwave and vibrational study of various isotopic species of vinyldifluoroborane was completed. The results of this study are presented herein. Experimental Section The synthesis of FzB(C2H3) has been previously presented in Three separate syntheses were carried out in order to obtain the deuterated species of vinyldifluoroborane used in this investigation.lb In each of the three syntheses, the series of reaction steps was the same. Vinyl bromide was prepared by the gas-phase reaction of acetylene and hydrogen bromide. The hydrogen bromide species were purified by passage through a -112 "C trap. Vapor pressures of 30 Torr a t -112 "C were used as a check of purity (lit.5 28 Torr). Reactions of 1:l mixtures were carried out in 2- or 3-1. gas bulbs with reactants in amounts that would keep the total pressure less than 1atm. The reactions required uv radiation to proceed a t ambient temperatures. The primary product, vinyl bromide, was separated from the dibromoethane species by fractionation through -78, -112, and -196 "C traps. Vinyl bromide was collected in the -112 OC trap and exhibited a vapor pressure of 420 Torr a t 0 "C (lit.5 424 Torr). Vinyl bromide was used in the preparation of a Grignard reagent by adding it to a solution of dry T H F and powdered magnesium in an inert N2 atmosphere. Stannic chloride was then added to the reaction flask. After the completion of the reaction, the volatile products were pumped through a -50 "C trap. The material that remained in this trap was purified on a low-temperature sublimation column.6 The pure tetravinyltin was characterized by infrared and mass spectra. The tetravinyltin was then condensed into a reaction flask along with an appropriate amount of BF3 which had been purified by passage through a -112 "C t r a p The flask was sealed off and heated to 60 OC for 16 h. At the end of this period, the volatile products were pumped off and purified by fractionation on a low-temperature column. Vinyldifluoroborane exhibited a vapor pressure of 562 Torr a t -45 OC and was characterized by infrared and mass spectra. In the first synthesis, deuterated acetylene was prepared by the reaction of DzO and CaC2 under Ar flow. The mass spectrum of the product indicated that its composition was -88% C2D2 and -12% C2DH. After subsequent reactions, the vinyldifluoroborane obtained was found to be -44% each of the cis- and trans-vinyldifluoroborane-d2species, -6% of the a-dl species, and -3% of each of the P-dl species. The second synthesis was designed to yield large amounts of the p-dl-vinyldifluoroborane. This was accomplished by allowing DBr to react with CzHz to produce 0-dl vinyl bromide. Finally, pure FzBCDCDz was prepared using a sample of C2D2 whose isotopic purity was raised from -88 to -97% by exchange in a NaOD-DZO solution. The purity of FzBCDCDz produced from such a sample of C2Dz was determined from infrared, Raman, mass, and microwave spectra to be better than 97%. The microwave spectra were recorded with a HewlettPackard 8460A MRR microwave spectrometer, using a Stark modulation frequency of 33.33 kHz. Frequency measurements were made with the Stark cell at room temperature or cooled
1189
with dry ice. Scans to both high and low frequency were made to achieve frequency accuracy to f0.02 MHz. Infrared spectra were recorded from 200 to 4000 cm-l by using a Perkin-Elmer Model 621 spectrophotometer or from 450 to 4000 cm-l by using a Digilab FTS-15B interfer~meter.~ Atmospheric water vapor was removed from the spectrophotometer housings by flushing with dry nitrogen. In the high-frequency region, the instruments were calibrated in the usual manner,s$gwhereas the lower frequency region was calibrated with atmospheric water vapor and the assignments of Hall and Dow1ing.l" The infrared frequencies are believed to be accurate to f 2 cm-1. Cesium iodide plates were used as windows for the gas and cold cell as well as the substrate for the low-temperature experiment with the Perkin-Elmer Model 621 while potassium bromide windows were used in the interferometer. Raman spectra were recorded on a Cary 82 Raman spectrophotometer equipped with a Coherent Radiation Model 53A argon ion laser. The Raman frequencies are known to f 2 cm-'. The spectrum of the gas was recorded using a standard Cary multipass gas cell. The Raman spectra of solid F2B(C2D3) were obtained by using a Harney-Millerll type cell, cooled with the vapors of boiling liquid nitrogen. Raman spectra of liquid F2B(C2D3)were obtained using sealed glass capillaries, The 5145-A laser line was used with the power a t the sample varied between 0.5 and 2 W depending upon the physical state being examined. Spectra of the gas are shown in Figure 1with Raman spectra of the liquid and crystalline solid states of F2BCDCD2 shown in Figure 2. Microwave Spectrum and Assignment The spectra of the various isotopic species reported were assigned as A-type rotors with R-branch transitions dominating the spectra. B-type $-branch transitions were found to be very weak and, therefore, undetectable for many of the species of lesser abundance. The moments of inertia reported in our initial report2 were adjusted as necessitated by recent improvements in the values of physical constants to give 52.465,131.745, and 184.243 u AZin F211BCHCH2 and 52.464, 131.593, and 184.094 u A2 in FzlOBCHCHz or I*, Zg,and I C , respectively. The microwave data for the additional 12 isotopic species are listed in Tables 1-111 (miniprint material; see paragraph a t end of text regarding miniprint material). In addition, the three most intense satellite lines for the F211B12CD12CDz species were also assigned, and these data are given in Table IV (miniprint material). The relative intensities and inertial defects, A, were found to be analogous to the corresponding excited state lines of the protonated species. The arguments applied to the assignments of these lines to the respective vibrations is based on the observed inertial defects as given in the earlier work2and will be discussed in a subsequent section. The observed transitions were, in each case, fit to the rigid rotor model using an iterative least-squares computer program. The moments of inertia were obtained from the rotational constants using the conversion factor 505 379 MHz amu A2. All of the O ' B and 13Cdata were measured from species in natural abundance. Since these weaker species are often obscured by vibrational satellites, measurements were taken on only those lines which were not overlapped by excited state satellites. Structure The preparation of mono-, di-, and trideuteriovinyldifluoroborane and the natural abundances of 1OBand 13Cisotopic The Journal of Physical Chemistry, Voi. 80,No. 11, 1976
1190
Durig et al.
-
Obrd Ohid . c a l c d -~
32,971.41
-0.11
-
'41 * '40 '15 * '14 '24 423 533 432 '32 * '31 514 413 523 * 422 '05 * '04 '16 * '15 505 + 506 ' 2 5 + '24 615 * '14 624 * 634 * 533 f
-
-
33,025.10
-
0.01
34,534.31
0.09
35,075.47 35,722.30 18,559.97
0.00
-
-
-
0.05 -0.02
-
-
-
9.541,92 :0.07 3,808.85 0.02 2.721.89 i 0.02 -0.651240 52.964 :0.004 132 556 i 0.002 185.672 i 0.002 0.023
*
5 C IR
15 IC
-
-
3i2+211 '14 * '13 404 * 303 423 * 322 422 * %1
-
lis * 312
-
0.02
26,987.63 505 * 414 26,915 85 i15* 4,4 28.218.85 iO5 + ilO429,044.68 524 + ilZ3 31.126.65 5j3 432 31,860.41 632 * IPl32,132.58 ill 413 33.355.45 523 + 422 33.638.1~ 616+jli 606 * '06 -
-0.19 0.39 0.15
0.06 -0.10 -0.06 -0.11 0 13
~
f
-
-
KI6 * 5 0 j
36,664.33
634 * 533 525 * 524 533 * 532 615*j14 725 I707 '07 * '16
-
-0.23
-
-
-
0.01
33,565.72
707 * 606 '17 * '08
0.12
-
-
-
31.4SI.61 31.390 95 27,705.93 31.956 87 32,515.71 35,091.71 37,319.16 38,076.77
35.050.38
29,458.85
0.lC
0.15
31.527.73
0.18 0.05
-
0.11
0.00
32,022.92
0.10
-0.06 -0.07 -0.04 -0.02 -0.31
8,553 74 :0.5 3,452.81 j 0.01 2,484 08 I 0 01 -0.6'1581 1 57.081 :0.003 146.355 I 0.001 203.447 I 0,001 0 001
-
-
-
27.546.51 28,442.70 30.213.22
-
0.09 0.12 -0.01
-
32.331.01
0.03
32,252.10 32,533.35
-0.07 0.07
33,4151.11
0.00
-
-
-
Obrd Obrd - c i l c d -~ -
0 13
-
~
A
Obrd Obrd - c a l c d -~ 26,829.21 29,420.77
33,336.09
0.01
37,536.06 38,481.28
0.05 -0.05
39,015.65
-0.11
-
-
-
-
8,853.59
30.022.09 31,304.65 31,222.05
-0.18
0.50 -0.27
0.24
22.762.55
23.825.33
-0.15 0.20
25.052.00 25,457.07
--
0.38
-
-
31,599.30 32,174.53
-0.09 0.06
-
-
-
-0.13
37,121.00 39,010.45
-0.37
-
-
-
533 * 532 616 * 5,4 624 * 523
8
c
* 0.019 * 0.003 * 3.003
A
30.557.23 -
3058 R 3031
;
2998 R
32,375.50 32,297.40
-
2991
L
h
s
1618
3
36,608.96
-0.04 -0.29 4.18 0.04 0.32
-
17,497.09 37.897.15 38.925.50 39,445.11
29,747.82 31,543.69 33,875.31
0.02 0.12 0.18
34,388.91 36,012.52 37,734.86 38,798.14
0.06 -0.20 -0.06
-
-
-
9 , 6 0 4 . 3 8 :0.8 3,575.35 0.02 2,605.51 i 0.02 4.722572 52.620 I 0.005 141,311 I0.002 193,965 i 0.002 io.034
-
33,534 06 3L.270.59 36,549.66 37,512.06
-0.23
-
9,425.91 i 0,9 3,720.44 t 0.03 2,667.21 i 0.02 -0.688332 53.616 z 0,005 135.838 i 0.002 189.479 0.002 10.025
*
0.11 -0.21 -0.06 .0.28
9.603.31 i 't.1 3,581.12 3 0.03 2.601.96 i 0.02 -3.721795 52.622 0.007 141.123 x 0.002 193.783 I 0.002 10.035
*
3107
b1
CH2 a a t l r m i t ? (30011
3018
v2
:H2 rym i t ? (9311. C-H
VI
-
1422 VI 1350
P
2590 I
1625
p
1520 V I P
VI
-1440 b,rh -
do
1426 m
VI
P
-
p
2992 m
2331
VI
C - H str 19311, C H 2 iym i t ? (7%1
1520
1528
I 4 4 0 r h p 1446 m -
1426 m P
-
1350 w
p
m
-
1425
r
-
-
SIP
!7X)
C=C itr I I L I I , C-5 ST? 13151. C-H i n - p l a n e !l5$i
"1 b e i d
-
1432 1429 1382
-
l3L0 m
P
1332
P
1330 m
1351
1318s
p
13178 P
13065
1329
1255 vw
0
1259 v d
1259 vk
-
-
1258 R 1250 9 1242 P 1027R 1015 9
9.074.86 3 0 . 0 7 3.552.14 I 0.03 2,552.57 1 0 . 0 3 -0.693490 65.690 * 0.001 142.275 i 0.002
195.180 b 0.001 i0.017
193.795 i 0.005 10.028
197.988 10.023
I
0.003
See TLble I.
refer t o the w l i i t i v e p 0 r i t i o n i o f The t w o 'H a t o m w i t h r e s p e c t t o the double bond
molecules has made it possible to determine substitution coordinates for some of the atoms. The r, parameters and their errors were calculated by the single-substitution method as outlined by Kraitchman12 and Costain13and, in certain cases, by the double-substitution method of Krisher and Pierce.14 The following values have been obtained rg-c = 1.533 f 0.008, rC,H = 1.083 f 0.009, and LHCB = 123.1 f 1.5O. The coordinates of the fl protons were also determined, but the data for the /3 carbon-13 species were questionable and not included in the calculations or tables. The structural parameters given in Table V have been determined from a least-squares fitting of the experimentally determined moments of inertia. Initially, the rs coordinates were used as constraints in the calculations. Bonded and nonbonded distances determined from substitution coordinates were held fixed while the least-squares routine varied the remaining parameters in fitting the moments of inertia of the 15 isotopic species. After the structure seemed to have been optimized within these constraints, all the parameters were allowed to vary. The program allows for the moments of The Journal of Physical Chemistry, Vol. 80, No. 11, 1976
0.05
-
37,575.58 38.367,40
8,881.43 i 1 . 4
0.001
-
33.500.53
-
3.692.65 2 0.05 2,607.79 I 0.05 -0.654185 66.903 0.009 136.864 0.003
i
-
0.03 -0.07 -0.21
2331 V L
1375
9.074.90 i 0.03
& and
RIB w
1624 9 1632 R 1615 P
-
3,547.19 i 0.01 2.550.10 3 0.0,1 -0.694369 55.690 I 0,001 142.473 i 0.001
*
-
37.072.52
i
193.977 t0.017
2991 9 2584 P
33,513.40
T
*
-
-
1418
3.687.47
-0.655132 56.507 0.001 137.053 :0.001
-
-
0.02 C.00
2090 w
"W
I457 1450 1443 1425 9 I431
8,580.84 :0.01
IC
6
-
0.16 0.01
3014
2,605.35
1
anw
9
3083 P
B
I5
*
l6 iC
-
28,081.84 29,061.30
9,425 91 i 0.5 3,716.53 i 0.01 2,664.75 $ 0.01 4.659161 53.616 i 0.003 136,014 x 0.001 189.651 i 0.001 r0.021
55.596 L 0.003 112.n5 0.001 188.5ia= 0.001 *O.O16
la
-
0.09 -0.04
-
-
-0.65~18~ 57.455 147.150 204.159 0.114
C
la
0.17 0.15
9,050.27 i 0.4 3,601.38 i 0.02 2,680 22 i o . 0 1
A
VI 1255 VI 3236 "I
1263 b
P
1240 w
B C
w m
1021m
1024"
-
p
1 0 2 0 w dp
1015 s
c
5
995 I
-
989 9
0.01 0.01
0.C2 -3.05 -0.05 -0.18
-
R
i a b l e 111. Continusd
A
0.11
-
634 * 533
6
3.455.16 i 0.02 2.486.14 + 0.02 -0.694789 57.082 :0.004 146 141 + 0,001 203.230 I O . 0 0 1 0.007
0.08 -0.03
~
-0.28
+G
0.07
L16 * ilj34.585.55 6 0 6 + 5 C 5 35,139.4; jZ5 sP4 38,179.ie
-0.07 .O.E 0.13
27.325 57 28,735.51 29.720.84 31.608.78 33.836.60 33,784.53 34.326 06 34.961.13 37,654.18
0.13
-
-
15.136.11 17,336.58 38,134.72 36,100.01
4;4 * J I 3 23,402.92 41j* j12 515 d14 29,035.38 j O 6 + 404 zg.876.74 521 I E Z 3 32.052.87 jI4 f q13 34,353.45 523 t 422 9,57;.67
Table V I .
fnlrared,b mltd
901
-
-
-
C C
m
lOl7w 1001 w
I025 1019
397 x
975
522 97 61191
w w
448 Rm 435
B
-
Raman,b ialid
liliuil
-
766 I
p
163
I
C a l c u l a t e d A5rlgnment and p o t e n t i l i energy d i r t r i o u t i a n c 751
123
736 I 727 522 m
-
1241
-
3
434 R
Raman. gas 755 V I p
h
$6,
vh
753 w
533 37
-
-
1238
Contimed
Infrared,
751 9 723 9
p
424
m
-
y o C-6
i t r (28%1, BF iym itr l58%), CUP rock (511, C-H I n - ~ l i n eban8 (5x1
524
-
-
-
427
m
221m x195 vw
-
103
-
m
P
427 L
439 435
P
421
Y
-
m
413
"
p
214m p
217"
dp
-
-
dp
128 m dp
160 B 138 I 124 r h 00
2 x
-
431
217 194
-
106
L a t t i c e mode v l j BF2 t o r l i o n (BB7.1, 8F2 "a9 15%)
C-H o u t - o f - p l a n e bend i 7 S l .
I
ii I
t d t t l r e made5
"
49 w 42 32 m
aAbbreulationi used: 3 , r t r o n g i m. m t d l m i x, weak; v , vary; b. brold; I h , shoulder; p, p o l a r i z e d ; dp, depolarized. C r c f e r io ~ d p o phase i band :Ontairr.
A, B, and
b nata fake" from Ref. 2.
' Contrioutloni
O f l e s i than 4% Ire n o t i n c l u d e d .
inertia to be individually weighted. The ro structure given in Table VI (miniprint material) was calculated with the more poorly determined moments (some A moments and the 13C data) weighted less than one while the remaining moments were given weights equal to one. Errors inherent to the leastsquares procedure were calculated from the variance-covariance matrix and those reported in Table VI have been increased to account for the errors in the experimentally determined moments of inertia. The C-B bond is intermediate in length between those of CH3BF2 (1.60 A)15,16 and
Spectra of Vinyldifluoroborane
1191
*
404
27.747.36
524 1 4 2 3 523 -422 515 c S15
31,358.74 32.053.71
SO5
505 + SO5 625 I 524
-
515 + 514
32.675.22 35,103.59 37,296.03
'24 * 523
-
R
-0.07
-
-0.20 0.20 -0.29 0.27 0.09
-
8,778.9 I 1 . 1 3,444.29 = 0.03 2.492.62 I 0.03 -0.897223 57.557 f 0.009
8 C
1A 18 IC
146.730 d 0.002 202.750 i 0.003 -1.55
27,733.75 29.425.74 31,373.55 32.031.45
0.12 0.04 0.11 -0.01
32.555.01
-0.05
35,100.80
-0.05
-
38,047.45
-0.08
0.08 0.06
27,593.59 29.412.74 31.392.07 31,970.~ 32.599.58 35.081 . I 4 37,312.75 38.074.02
0.05 -0.05 0.03 -0.08
-0.02 -0.01
8,803.2 i 0.7 3,447.48 0.02 2,489.74 T 0.02
8,859.9 i 0.2 3,453.14 t 4.01 2,482.38 i 0.01
-0.696504
-0.695558
*
57.409
I
0.004
145.594 202.985 -1.02
I
0.001
145.353 I O . 0 0 1
57,0427 i 0.002
i
0.002
203.586 10.19
* 0,001
-
2217 0 2225 R A 2209 P
Y
2220 rn
1558 1562
I
lSi4
1558 sh
s
-
s
-
:1: ;ily
YYI
P
2251 VI
2240
v2
2216 VI
Q
2219 9
2199
u3 C-0 r t r (5811, COP s p I t l 14211
1552 w 1552 s h 1552
1585
-
:;1 ;
1560
-
-
-
-
8
s
1371 s
B
vs
1324
VI
I440
1370 I h
1343 I
1351 #
1301 VI
1313 s p
YS
1305 Q
, & i o-; lnlr
0
x
-
1023 R 1015 Q AI8 w 1009 Q
1027 Ih 1023 1020 t h
-
747 I 743 -
m Ih
9C
7
1
s
715 w
0
-
495 603 9R A I87 P 405 393 QR
1
0
x
m x
Y
YW
P
1323
-
u7 l08Fz
1302 m
-
1289
1M2 x
1073
1021 I h
-
1014 I
p
Q
Y
dp
807 m 185 v
dp
720 V I
Q
988
989
-
YX
815 m 185 m
747 w -
-
720 I
1014 1
Q
818 784
117 I
703
-
-
561 Y
-
497
491 x p
495 w
p
493
410 X
Q
439
P
-
414 m
397
p
401 Y
Q
412
m
397
345
344 Y W dQ
342
dQ
347
m
-
-
-
-
597 I 578 f 573 I
8
W
Y
~ 7 0 0YI
-
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11BF2 a n t i s m I t r (781). 8F2 10cX l i 3 1 1 . C-8 r t t l 9 1
Y7
ligF2 8F2 d sp c f (131). rtr l2iT8F2 1 3 c-c ; R t i9tr s m (38x), i t r 1111)
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--
~
mtlmm f t l 17911,
~m~ f l(2011, C-C I t l (4411, C-5 r t r i l 5 1 1 , BF2 d e f 113x1. 108F2 antirym sir (1011
-
-
-
658
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-
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_
-
--
-
38
e
-
-
-
198 m Q 185 YY dp
199 m
Q
190 YI dQ
200 m
143 x 122 m
-
-
97 v 59 Y
198 183
-
91 -
F o r a b b r t v i a t l o n f used, see Table V I l . C o n t r i b u t i o n s o f 1111 t h i n 4% w e n o t i n c l u d e d
B
j I
I
I
I/ L
3000 2000 1000 WAVENUMBER (CM-'1
Ab-.
Figure 2. Raman spectra of (A) liquid and (B) solid vinyldifluoroborane-d3.
L
3000 2000 1000 WAVENUMBER (CM-') Figure 1. (A) Infrared and (B) Raman spectra of gaseous vinyldifluoroborane and (C)infrared and (D) Raman spectra of gaseous vinyldifluoroborane-d3.
19s
1440 ~ .
~
1317
1343 w
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-
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-
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-
1350 w 1305
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-
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-
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758 152 748 735
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-
Symnetric CHZ r f r s t c h A n t i ~ y m t CH2 ~ l ~s t r e t c h C'C r t r e t c h c-H f t i e t t h C-9 I t r e t c h s y n e t r i c UF2 ifretch A n t l c y n e t r l c BF2 s t r e t c h Redundancy CH2 defonnatlon CH2 I n - p l a n e rock Redundancy CCB bend CH i " - p l m e bend Redvndanw B i z deformation CBF2 I n - p l a n e bend (BF2 rock)
2250
Q
1323 1315 0 R AI8
1064 1061
see i d b l e I
P
2217 I
-
-
sc$ t i154x1.c.0
2251 VI
H C d B F (1.513 A).17The CC distance is typical for ethylenic molecules.lS2l The B-F distances were allowed to vary independently at first, as were the C r H distances. We found that the leastsquares routine would "trade off' the B-F', C,-H,, and CrH' The Journal of Physical Chemktry, Vol. BO, No. 11, 1976
1192
Durig et al.
TABLE V: Structural Parameters for Vinyldifluoroborane
ro Parameters LCCB = 121.96 f 0.25 LH,CBb = 120.20 f 0.73 LH,C,Cp = 117.84 f 0.69 LH’CsC, = 119.50 f 0.36 LH’CpHb = 118.19 f 0.67 LHCpC, = 122.31 f 0.56 LF’BC = 121.72 f 0.48 LF’BF = 116.04 f 0.41 LFBCb = 122.24 f 0.63
= 1.532 f 0.003 rc=c = 1.339 f0.005 rCcHa = 1.086 f 0.007 rCB)-Hla = 1.087 f 0.006 rcB’-H = 1.087 f 0.006 TB-F’~ = 1.331 f 0.002 r B - F = 1.331 f 0.002 rB-C
rg-c rC,-H,
rs Parameters = 1.533 f 0.008 LH,CB = 123.1 f 1.9 = 1.083 f 0.009
H’ refers t o the proton that is cis t o the -BF2 group. F’ refers t o the fluorine atom closest to H’. These angles are implied by the values of the two adjacent angles. a
distances simply to reach a mathematical minimum. So separate additional calculations were carried out in which (1) the B-F distances were set equal and allowed to vary together and (2) both the B-F distances and Cp-H distances were set equal. The results of this latter calculation comprise Table VI. The former calculation gave results well within the errors of those in Table VI with r(Cp-H’) = 1.093 i 0.008 8 and r ( C p H ) = 1.082 f 0.008 8. It is not possible to tell if the C p H distances are actually different. In propylene,lg the corresponding distances were 1.090 f 0.003 and 1.081 f 0.003 8,respectively, as determined from substitution coordinates. We cannot tell if we are seeing a similar effect because both sets are within experimental error of one another. The B-F distances of 1.331 8 are consistent with those found in HCECBF~ (1.323 Vibrational Assignment The 18 normal vibrations of vinyldifluoroborane span the representation 13A’ 5A” of C, symmetry. The totally symmetric vibrations (A’) are all motions within the molecular plane and will give rise to polarized Raman lines and A, B, or A/B hybrid infrared, gas-phase band contours. Depolarized Raman lines and characteristic C-type band contours will result from the nontotally symmetric, out-of-plane A” vibrations. Assignment of the spectra was made using the Raman depolarization data, infrared gas-phase band contours, and group frequency correlations. Observed frequencies for F2BCHCH2 and FzBCDCDz are listed in Tables VI and VI1 (miniprint material), respectively. Typical spectra are shown in Figure 1.Spectra of FzBCHCH2 have been previously reported2 and those frequencies along with the frequencies for F2BCDCDz have been used in the normal coordinate analysis. Table VI11 summarizes the assignments of the fundamental frequencies of vinyldifluoroborane-do and -d3. The three C-D stretching modes can be clearly identified from the Raman spectra. In the gas phase the CD2 antisymmetric and symmetric stretching frequencies are at 2323 and 2261 cm-l. Even though both are A’ motions, the line at higher frequency appears depolarized. The CD stretch is assigned a t 2217 cm-l, which is the frequency of the Q branch of an A-type infrared band and a polarized Raman line. The C=C stretching vibration gives rise to a complex infrared band with local maxima at 1568 and 1562 cm-l while the Raman frequency is 1563 cm-’. The B-F stretching motions in FzllBCDCDz are found to be only slightly shifted from their corresponding frequencies
+
The Journal of Physical Chemistry, Vol. 80, No. 11, 7976
TABLE VIII: Fundamental Vibrational Frequencies (ern-’) of Vinyldifluoroborane and Vinvldifluoroborane-d2 Approximate description
FpBCH CH2
FzBCD CD2
CHz(CD2) antisymmetric stretch CH2(CD2)symmetric stretch CH(CD) stretch C=C stretch CHz(CD2)scissors l0BFz antisymmetric stretch llBFz antisymmetric stretch l0BFz symmetric stretch l’BF2 symmetric stretch CH(CD) in-plane bend CH2 rock B-C stretch BF2 scissors CBF2 bend (BF2 rock) BCC in-plane bend
3091 3021 2991 1624 1425 1425 1375 1338 1318 1250 1021 765 538 427 215
2323 2261 2217 1565 1068 1418 1369 1352 1315 1015 786 720 495 397 198
CHz(CD2) twist CHACDz) wag CH(CD) out-of-planebend CBF2 bend (BF2 wag) BF2 torsion
1015 989 729 198 103
748 802 566 185 95
in the “light” molecule. The infrared spectra of the gas show very strong absorptions between 1300 and 1430 cm-l. The B-type band whose central minimum occurs at 1369 cm-I is assigned to the antisymmetric 11BF2 stretch. The A/B hybrid infrared band having a Q branch at 1315 cm-l corresponds to a medium intensity Raman line a t 1313 cm-l and is attributed to a symmetric llBFz stretching motion. The lOB counterparts of these modes are also identifiable. Their respective band types are identical and the antisymmetric and symmetric vibrations occur a t 1418 and 1352 cm-l, respectively. Using these data, it is possible to verify the assignment of these modes in F2BCHCH2. The antisymmetric and symmetric llBFz stretches have been assigned at 1375 and 1318 cm-1.2 The 1°BF2 symmetric motion has been identified in the Raman and infrared at 1338 cm-le2The antisymmetric motion for the loB isotope must fall in the region of the CH2 scissors. The scissoring motion is assigned to the medium intensity polarized line at 1425 cm-l in the Raman spectra. The infrared shows maxima at 1418,1431, and 1443 cm-I around the 1425-cm-l Q branch of the CH2 scissors. The 1°BF2 stretch is expected to be a B-type band and could show maxima at 1418 and 1431 or at 1431 and 1443 cm-l. We prefer the former assignment on the basis of the intensities. The CD2 scissors in FzBCDCDz is assigned to a complex A/B .hybrid centered a t 1068 cm-l. The CD in-plane bend gives rise to the A/B hybrid band in the infrared whose Q branch appears at 1015 cm-l. There is also a corresponding Raman line a t 1014 cm-l. The remaining CH(D) bending mode of A’ symmetry is the CHz(D2) rock. In the previous study2 the CH2 rock was assigned to a Q branch a t 1015 cm-l that seemed to be part of an A-type band with the R branch at 1027 cm-l. For some time it has been felt that the CH2 rock in vinyl fluoride (FCHCHz) was very close in frequency to an out-of-plane rnoti0n.229~3Only recently it has been determined, using matrix-isolation techniques, that these two modes are within 8 cm-l of each other.24In F2BCHCH2, the 1015-cm-l Q branch
Spectra of Vinyldifluoroborane
1193
The assignments outlined above are supported by the recould be a C-type band arising from an out-of-plane mode sults of Teller-Redlich product rule calculations. The theowhile the 1027-cm-l band is the R branch of a B-type band retical 7 values for the A’ and A” blocks are 7.305 and 2.520, whose P branch would be expected around 1013 cm-’. This respectively, while the observed ratios are 7.213 and 2.501. The assignment is supported by the appearance of a polarized line results are good and the errors are within the limits set by the at 1021 cm-l in the Raman spectrum of the gas. In the -d3 experimental accuracy of the frequencies. compound the only assignment for the CD2 rock is at 786 cm-l. This appears as a shoulder on the side of the 807-cm-l Normal Coordinate Analysis line in the Raman spectrum of the room-temperature liquid, The normal coordinate calculations were carried out using but, as the liquid is cooled, the line becomes more distinct, and the programs of Schachtschneider29which employ the stanis clearly a separate fundamental in the spectra of the crysdard Wilson FG matrix method.30The 21 internal coordinates talline solid. The alternative assignment for this motion is the consisting of the bond lengths, bond angles, out-of-plane wags, A-type band centered a t 691 cm-l. This would give a shift and torsions shown in Figure 3 were used as a basis for the factor of 1.48 so we prefer the former assignment. vibrational analysis. For the purposes of minimizing the Skeletal motions comprise the remaining four A’ fundanumber of force constants and simplifying the force field, local mentals for the F2BCDCD2 molecule. The B-C stretch is asCzUsymmetry was assumed about both the =CH2 and -BF2 signed to the strong polarized Raman line at 720 cm-l. The groups. The symmetry coordinates used are listed in Table BF2 scissoring motion gives rise to an A-type infrared band IX (miniprint material). A preliminary normal coordinate centered at 495 cm-l with a Raman coincidence a t 497 cm-l. calculation using the 21 diagonal force constants implied by The CBF2 in-plane bend (BF2 rock) and BCC in-plane bend the internal coordinates showed mixing of modes to be quite are assigned to polarized Raman lines at 397 and 198 cm-l, strong in both symmetry blocks; thus, a simpler force field was respectively. sought to accommodate the possibility of using more interThe A” vibrations produce dipole changes perpendicular action force constants and fewer diagonal force constants. It to the molecular plane and give rise to C-type Q branches in can be seen that the number of force constants used in the the infrared spectra of the gas. In the infrared region invesforce field exceeds 3N 6, but in view of the isotopic data we tigated there are four apparent C-type bands for F2BCHCH2. obtained, not only for deuterium but also boron substitution, These occur at 1015,989,751, and 729 cm-l. In F2BCDCD2 we feel justified in using this number of force constants. the only certain C types are a t 748 and 711 cm-l. The three The frequencies calculated by using the force constants motions that must be assigned in this region are the CH2(CD2) given in Table X agree with the experimental ones to anavtwist, the CHz(CD2) wag, and the CH(CD) out-of-plane bend. erage of 8.4 cm-l (l.O??). For the out-of-plane vinyl vibrations, Potts and have tabulated group frequencies for CH the force constants are very similar to those for C Z H ~ B ~ . ~ ~ out-of-plane bending modes. They find that the twisting Additionally KQhas a value characteristic for carbon-carbon motion for vinyl compounds occurs in the region 920-1020 double bonds. The potential energy distributions given in cm-l while the CH2 wag is between 830 and 970 cm-l. They Tables VI and VI1 show considerable mixing. The C=C also find that the wagging motion is stronger in the infrared. stretch is mixed with the C-H bending modes, as well as the The CH out-of-plane bend falls at lower frequencies and deC-B stretch, in the A’ block. Additionally, we find that the pends heavily on the substituent. The designation of the C-B and B-F stretching motions are mixed to the extent that twisting and CH out-of-plane motions as such is for convenience since these motions are heavily m i ~ e d . ~For ~ > these ~ ~ i ~it~is difficult to identify them as separate modes. The outreasons we assigned the CH2 twist to the band a t 1015 cm-l of-plane motions show the expected mixing of the CH2 twist, wag, and the CH out-of-plane bend.23$26 and the wagging motion to the strong bands at 989 cm-l in the In view of the low molecular symmetry, we feel that the -do species. We would like to assign the twisting vibration in force constants obtained are reasonable and the PED is valid F2BCDCD2 to the weak depolarized Raman line a t 802 cm-l for describing the molecular vibrations in a quantitative in the gas phase and the CD2 wag to the strong C-type Q branch in the infrared at 748 cm-l. On the basis of the normal fashion. coordinate analysis, however, we will reverse this assignment, Discussion although there is substantial mixing of the modes. The The interest in assessing the T character of B-C (ethylenic) CH(CD) out-of-plane modes fall at 729 and 566 cm-l in the bonds has prompted our more thorough investigation of infrared spectra, respectively, and show the expected shift. vinyldifluoroborane. The recent 13C NMR study3 of the Cb The remaining vibrations are the CBF2 out-of-plane bend shifts indicated more delocalization of the double bonds in the (BF2 wag) and the BF2 torsion. These are assigned in monovinylhaloboranes than in the divinylhaloboranes. FzBCDCDz by analogy to the “light” compound and occur at Variations in bond lengths might be expected to parallel the 185 and 94 cm-l, respectively. The intensities of microwave satellites aid in these assignments as well as with the assigntrends in the chemical shifts. Our microwave data indicate that the C=C bond length of 1.339 f 0.005 %, in vinyldifluoment of the V I 3 fundamental. The inertial defects associated roborane is within experimental error of the corresponding with these three excited states (Table IV) indicate that they arise from two out-of-plane motions and an in-plane motion. propylene (1.336 distance in vinylfluoride (1.329 f 0.006 The intensities predict vibrational frequencies of 85 f 20,196 f 0.004 A),19 vinyl chloride (1.332 f 0.002 and acrylo& 20, and 193 f 20 cm-l for Y 1 8 , ~ 1 7 and , ~13,respectively. nitrile (1.338 f 0.009 This consistency of bond lengths The barrier to internal rotation about the C-B bond was may extend to vinylsilane and vinylgermane, as well, in which calculated as has been previously d e ~ c r i b e d . ~We ~>~ find * a these values are 1.347 f 0.00331 and 1.347 f 0.015 A,32 revalue for the twofold barrier to internal rotation of 1546.5 f spectively. We may conclude that the C=C distances in vinyl 81.6 cm-l (4.42 kcal/mol) using F values represented by F ( a ) compounds are insensitive to substituents. Thus, it is not = PO Zn116 F, cos na,where Fo = 1.7273, F1= -0.011 19, surprising that evidence for delocalization cannot be found and F2 = 0.1388 for the -do species and Fo = 1.3160, F1 = in this structural parameter. In acrylonitrile (H&=CH-CN), -0.007 81, and F2 = 0.070 77 for the -d3 species. for instance, the C-C bond (1.425 f 0.006 A) is shorter than
-
+
The Journal of Physical Chemistry, Vol. 80, No. 11. 1976
Durig et al.
1194
e l
Figure 3. Internal coordinate definitions for vinyldifluoroborane.The CHp twist, T ~and , BF2 torsion, T ~are , not shown.
TABLE X: Internal Force Constants for Vinsldifluoro borane Force constant
KR KQ Ks Kr K,, H, Kor Ha H, H4
H+p H, Hx H, H,
HT, HT,
Fw FQ, FS6 F,,, a
Grour, CH2 stretch C=C stretch CH stretch CB stretch BF2 stretch LHCH bend LHCC bend of CH2 LHCB bend LCCBbend LHCC bend of CH ~FBCbend LFBF bend CH2 out-of-plane bend BF2 out-of-plane bend CH out-of-plane bend CHz twist BF2 torsion CB stretch/BF stretch C=C stretch/HCH bend C=C stretch/CH bend CH out-of-plane/CHz twist
Value. mdvn/Aa 5.10 f 0.01 8.25 f 0.04 4.86 f 0.01 5.59 f 0.05 5.20 f 0.02 0.426 f 0.003
0.555 & 0.003 0.311 & 0.007 0.484 f 0.018 0.658 f 0.006 0.753 f 0.012 1.64 3= 0.03 0.287 f 0.003 0.055 & 0.002 0.302 f 0.004 0.211 f 0.002 0.016 f 0.002 0.861 f 0.024 -0.595 f 0.014
0.344 & 0.020 -0.131 f 0.003
All bending coordinates weighted by 18.
a “normal” single bond (1.526 A), while the multiple bonds are unaffected. It is equally difficult to evaluate the implications of the C-B distance. The length of the C-B bond in vinyldifluoroborane is bracketed by the corresponding distances in CH3BFzl5J6 and HCCBF2.17 As pointed out by Lafferty and Ritter17 this may be a consequence of the hybridization around the carbon atom. The amount of s character of the C-B bond increases as one follows the series CH3BF2, F2BCHCH2, and HCCBF2, with sp3, sp2,and sp hybridization, respectively, of the carbon. Multiple-bond character would be expected to compliment this effect and is difficult to assess for this reason. The lengths of the B-B bonds may be an indication of some delocalization of the ethylenic double bond. In vinyldifluoThe Journal of Physical Chemistry, Vol. 80, No. 11, 1976
roborane, this distance (1.331 f 0.002 8) is the longest yet reported for a tricoordinated boron atom. In HBF2, HCCBF2, and BFzOH these distances are 1.311 f 0.005,331.323 f 0.005,17 and 1.32 f 0.02 respectively. Back donation of a-electron density from fluorine to boron presumably gives rise to the short bond in HBF2. In FzBCHCHz a ?r donation from the vinyl group can be thought of as competition for the effects of fluorine donation. If this were the case, the B-F distances would be expected to lengthen slightly. For tetrahedrally coordinated boron atoms, B-F distances are longer (H3PBF3, rB-F = 1.372 In our structural calculation we constrained the B-F bonds by requiring them to be equal. It still seems clear that the differences between these lengths in the above series are real. The immense amount of data required to determine B-F distances may limit its usefulness as an indicator of the amount of delocalization of the vinylic a electrons. The vinyl force constants derived for vinyldifluoroborane (Table X) are not strikingly different from those in other substituted ethylenes. The C=C stretching force constants is smaller than the currently accepted value in ethylene (9.147 mdyn/&,36 while the CH2 stretching constants are essentially the same. The force constants for the CH out-of-plane motions are in the same ranges as those in vinyl vinyl bromide,26and ethylene.26However, the twisting force constant in vinyldifluoroborane is somewhat smaller than in these other compounds. There also seems to be more mixing among the three vinyl out-of-plane modes in this case than in the other molecules, and we find that the amplitudes of vibration are also larger. Again, it is difficult to say whether these features are indicative of delocalization of the C=C bond. As pointed out in the earlier work: the barrier to internal rotation about the C-B bond is typical for twofold barriers and provides little information about the a character of this bond. The revised value of 4.42 kcal/mol for this barrier is slightly higher, but within experimental error of the previous value of 4.17 kcal/mol.2 The difference between the barriers calculated from the data for FzBCHCHz and F2BCDCD2 must arise from the mixing of the torsion with other normal modes. Excellent consistency is generally found for barriers in “light” and “heavy” molecules when the torsional modes are “pure”. The errors in measuring the torsional frequencies in vinyldifluoroborane may be as large as 3 cm-l because the upper level “hot-band” transitions are separated by less than 1 cm-l. Since a number of excited vibrational states are expected to be populated a t room temperature for a vibration of such low frequency, these “hot bands” can cause the maximum to be displaced from the fundamental frequency. The spectra of the crystalline solid show some interesting features. The number of lattice modes in FzBCHCHz indicates that there are a t least two molecules per unit cell. It is not reasonable to assign these lattice modes specifically to librations and translations since the differences between the isotopic shift factors are less than those implied by the f2-cm-l error of the frequencies. It is interesting to note the seemingly anamolous shifts upon condensation of the BF2 torsional and antisymmetric stretching modes. The torsion shifts more than 30% in each case to higher frequency. Ordinarily shifts of 10% are noted for methyl r o t o r ~ , 3but ~ we can expect a more pronounced effect for a planar molecule because of crystal packing considerations. The antisymmetric BFz stretches shift by -45 cm-l while the symmetric modes only shift -12 cm-’. Again, this must be a consequence of the crystal packing and the nature of the motion involved. We can conclude by summarizing our results. It is not
Ir Behavior of Fine Particulate Solids
possible to state unequivocally whether there is delocalization of the a electrons of the C=C bond. There are subtle indications that this might indeed be the case, but the “classical” indicators do not imply this. The C=C bond is of “normal” length, but the B-F distance may be somewhat longer than expected. There are no values with which to compare rC-B to assess that bond’s a character. The normal coordinate calculations may indicate some delocalization, but the complex mixing of the normal vibrations makes this difficult to assess as well. This study neither contradicts nor confirms the conclusions drawn from the NMR data? It is possible that NMR is a more sensitive technique for drawing these conclusions. It may be necessary to revise the classical theories concerning delocalization and structure.
Acknowledgment. The authors gratefully acknowledge the financial support of this work by the National Science Foundation by Grant No. MPS74-12241-AO. Miniprint Material Available: Full-sized photocopies of Tables I-IV, VI, VII, and IX (10 pages). Ordering information is available on any current masthead page. References and Notes (1) (a) J. R. Durig received his Ph.D. from M.I.T. under the direction of Professor Lord in 1962. (b) Taken in part from the thesis of L. W. Hall which was submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May, 1975. (c) C. J. Wurrey received his Ph.D. from M.I.T. under the direction of Professor Lord in 1973. (d) V. F. Kalasinsky received his S.B. degree from M.I.T. under the direction of Professor Lord in 1972. (2) J. R. Durig, R. 0. Carter, and J. D. Odom, lnorg. Chem., 13, 701 (1974). (3) L. W. Hall, J. D. Odom, and P. D. Ellis, J. Am. Chem. SOC.,97,4527 (1975). (4) F. E . Brinckman and F. G. A. Stone, J. Am. Chem. Soc.,82, 6218 (1960).
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Infrared Spectral Behavior of Fine Particulate Solids Graham R. Hunt’ U S . Geological Survey, Denver, Colorado 80225 (Received January 12, 1976) Publication costs assisted by the U.S.Geological Survey
Transmission and emission spectra of clouds and layers of fine particulate samples of quartz, magnesium oxide, and aluminum oxide in the 6.5-35-pm wavelength range are presented. They demonstrate that the behavior of layers of particles constitutes a good analogue for a cloud of particles; that individual micrometersized particles emit most where they absorb most; that as the size of the particle is increased, the emission features reverse polarity and the spectrum approaches that of one obtained from a polished plate; and that as the particle layer-thickness increases, radiative interaction becomes increasingly important so that the emission maximum shifts from the strongest to weaker features, or produces a maximum at the Christiansen wavelength.
Introduction The appearance of the spectrum of a cloud, or layers of micrometer-sized particles, cannot be simply related to the optical constants of the bulk material in the same way as can that of a polished plate of the substance. In addition to the
absorption and refractive indices, other parameters, such as particle size and shape, size distribution, particle density, cloud or layer thickness, and the thermal distribution throughout the sample all have an effect on the appearance of the spectrum. The Journal of Physical Chemistry, Vol. 80, No. 11, 1976
