NOTES
284 suming the presence of A113.QEtzand rapid exchange. Although other complexes cannot be completely ruled out on this basis, their importance would require further rationalizations of the nmr data. A small amount of AIIa. (QEtz)z might be an important intermediate in the rapid ether exchange. This work shows that complexed aluminum iodide is the important initial solute species in diethyl ether. The similar observa,tionsfor A1Br3and AlCl,4-a indicate that etherate complexes are formed in solution near room temperature in all these cases. Assignment of 27AInmr spectra in such systems to A l a e has been based primarily on line width cox is id era ti on^.^^^ Reassignment of these spectra to AIXs*OEtzis required in the case of aluminum iodide aiid may well be warranted for other ether-halide Fysteins not examined in the present work, The stability of A113.0Etz solutions depends on several factors. Samples prepared in the present work were water-white and apparently stable for a t least 12 hr i n vacuo at room temperature. Both solutions and solid slowly decompose in air, first turning yellow, then brown. The presence of Iz impurity catalyzes a slow ether cleavage in this system, leading to an observed ethyl iodide p r ~ d u c t . ' ~Rapid thermal cleavages leading to mixed1 a1uniinum halide-alkoxides have been reported for several systems at elevated temperatures'* and could be assisted by the heat released during complex formation if nltxtures were not cooled. Some of these processes may account for the slow changes at room temperature observed by 27Al nmr in some of these systems, Achnowledgment. We wish to thank Research Corporation for support of this work through the Cotrell grant, program. We also wish to acknowledge both the work of Dan Quarks, Maryville College, on some of the initial phases of this study, and the generous assistance of Mr. William Peed of the University of Tennessee at Knoxville in obtaining the nmr data. (13) P. J. Oyren and J. !P. Cannon, in progress. (14) See reference 1, Vol, 4, Chapter 47.
Chemical HF 1,as;ersfrom NFI-H~and
NF3-C2Hs Systems by 11.C. Lin Chemical Spectroscopy Section, Naval Research Laboratory, Washington,D.C'. 905530 (Received August $6, 1970) Publication costs assisted by the Naval Research Laboratory
Chemical HF lasers based on the elementary reaction
F
+ H2+I7F' $- H
(AH10 = -32 kcal/mol)
T h e Journal of Physical Chemistry, Val. 76, No. 3,1971
(1)
have recently been produced from the flash photolysis or pulsed electrical discharge of various fluorine-containing compounds in the presence of H2.1-5 Laser action initiated at high temperatures by shock waves has also been reported;6 and, most recently, continuous-wave (cw) emission resulted from a very rapid mixing of F atoms produced either from the dissociat,ion of SFs with a high-current density arc7or from the dissociation of Fz initiated by an rf discharge or by the reaction of NO.8 I n this note, we report the results of a chemical HI? laser obtained from a repetitive pulsed electrical discharge of the mixtures of KFa H, or NF3 C2Na. Six vibrational-rotational transitions from Av = 2 1 were observed in the former system and a total of ten lines, with six from 2 1 and four from 1 -t 0 transitions, were identified in the latter. A t the inception of this work, it was learned that the flash photolysis of NF3 HB mixtures did not lead to laser action, whereas initiation by a high-energy electron beam of 1.2 MeV led to a single line oscillation a t Pzl.39D The experimental setup was similar to the one described previously.1° The reaction tube consisted of an 80 em long, 12-mm i.d. Pyrex tube maintained at room temperature. The emission was analyzed wit,h a 50-em NIodel 305-SNIP grating monochromator and detected with a Ge-Au cell operating at 77°K Electrical pulses were produced by switching two O.Ol-pF capacitors connected in parallel through a spark gap. The maximum repetition rate was 2.5 pulses/sec. The peak voltage employed was 4 2 5 kV and the pulse width a t half maximum was -2 psec. I . NR-HZ System. The results obtained from the NF3-H2 system are given in Table I, The observed frequencies are listed together with the calculated values'' for comparison. As mentioned before, oscillation in this system took place exclusively on 2 + 1 transitions, whicli always prevailed in the chemical laser
+
+
=+
+
(1) J. H. Parker and G. C. Pimentel, J. @hem. Phys., 48, 5273 (1968), and their previous work cited therein. (2) R. W. F. Gross, N. Cohen, and T. A. Jacobs, ibid., 48, 3821 (1968). (3) N. G. Basov, L. V. Kulakov, E. P. Markin, A. 1. Nikitin, and A. N. Oraevskii, J E T P Letters, 9, 375 (1969). (4) P. Gensel, K. L. Kompa, and J. Wanner, Chem. Phys. Lett, 5 , 179 (1970). (5) T. F. Deutsch, A p p l . Phys. Lett. 10,234 (1967). (6) R. W. F. Gross, R. R. Giedt, and T. A. Jacobs, J. Chem. Phgs., 51, 1250 (1969); J. R. Airey and S. F. McKay, A p p l . Phys. Lett., 15, 401 (1969). (7) D. J. Spencer, EI. Mirels, and T. A. Jacobs, ibid.,16, 384 (1970); M. A. Kwok, R. R. Giedt, and R. W. I?. Gross, {bid., 16, 386 (1970). (8) T. A. Cool. T. J. Folk, and R. Et. Stevens, ibid., 15, 318 (1969); T. A. Cool and R. R. Stevens, J . Chem. Phys., 51, 5175 (1969). (9) D. W. Gregg, et al., private communication through Professor S.H. Bauer. (10) M. C. Lin and S. H. Bauer, Chem. Phyrr. Lett., 7, 223 (1970); M. C. Lin, ibid., 7, 209 (1970). (11) P. A. Kittle and D. W. Placzek, Technical Report S-139, Rohm and Haas Company, Redstone Research Laboratories, 1967.
NOTES
285
Table I: Observed HF Chemical Laser Lines from the NFa-H2 System ---Frequency,
Relative intensity (Imd
cm-----. Calcdb
Transition
Obsda
Av=2%L P(4) P(5) P(6) P(7) P(8) P(9)
3622.0 3576.8 3530.3 3482.7 3435.0 3384.8
5 Slit width used was 0.25 mm. Placzek.
3622.6 3577.5 3531.2 3483.7 3435.0 3385.3
h
1.5 4.5 7.0 7.0 5.0 1.5
Calculated by Kittle and
emission produced from reaction 1. The absence of transitions with v > 3 probably indicates that reaction 2 H
+ KF3 -+
HF'
+ NFz (AHz"
=
-77 kcal/mol)
(2)
does not produce IXF with partial population inversion. A similar abstraction reaction, H UFB + HF UF5 (AH" = -46 kcal/mol), was also believed to be unimportant,l although H IF6 + H F IF4 ( A H " = -70 kcal/mol) was shown to be operative in laser emi~sion.~ Under the present conditions, the optimum pressure of NF3 was found to be P N FN~ 0.3 f 0.1 Torr. The pulse repetition rate depended rather strongly on the partial pressure of NFS; however, it varied only slightly with Hz or He pressure. The effects of Hz and He on the total emission intensity are shown in Figure 1. It is seen to be extremely sensitive to He, which, however, has an opposite effect on the emission from the NFaC2H6 system, as will be discussed later. With P N F=~ 0.20 Torr, the threshold pressure of Hz is about 1.1 Torr and the optimum output occurs at P HN~ 1.6 Torr, in the absence of He. The decrease in output a t higher H, pressure, i e . , P H ~> 1.6 Torr, can be readily accounted for by the deactivation of a vibrationally excited H F by Hz via the V-V transfer process
+
+
HF(v)
+
+
+ H,(O) --+ HF(0 - 1) + Hz(1) ( A E = 380 cm-l)
(3)
Reaction 3 is expected to take place with a faster rate for lower v values. This might account, a t least partly, for the absence of 1 3 0 transition in the NFa-Hz system under our preaent conditions. This argument is further supported by the fact that addition of HZtends to eliminate the 1 a 0 transitions of H F produced in a transverse electrical pulsed discharge of freons. l 2 11. NF3-C2He System. The reaction of F atoms with various hydrocarbons has been investigated by Parker and Pimente1.l I n their work, no significant
P (torr ) Figure 1. The effects of Hz and He on the total HF laser intensity: 0 , P N F=~0.20 Torr, Pa, = 2.10 Torr; P N F=~0.20 Torr; Pae = 0.
+,
difference was observed between the reaction of F with Hz, CHI, CzHe,and C3H8. I n this study, ethane was selected because of its immediate availability. The results obtained from this system are listed in Table 11.
Table I1 : Observed HF Chemical Laser Lines from the NFs-CZHe System -----Frequency, Transition Av=2-+1 P(4)-P(9) Av = l + O P(7)
W) P(9)
P(10)
ow5
cm-L-------Calcdb
See Table I 3643.9 3593.8 3542.1 3489.5
3644.3 3593.8 3542.3 3489.6
a The intensities of the 1 -+ 0 transitions were about 3 times Calculated by as strong as those of the 2 + 1 transitions. Kittle and Placzek."
A total of ten lines were identified, six 2 + 1 and four 1 --t 0 transitions. Each line in the latter transitions was found to be about 3 times as strong as the former. The significant difference between HZ and a hydrocarbon molecule has not been previously reported. It may be attributed to a molecular dynamical effect that can be best studied by a low-pressure chemiluminescence or molecular beam experiment. The reaction of atomic fluorine with CzHa
F
+ C&
+HFt
+ CzH6 (AHe" = -38 kcel/mol)
(4)
is 6 kcal/mol more exothermic than reaction 1. The ethyl radical produced above can undergo the following reactions. (12) M. C. Lin and W. H. Green, J. Chem. Phys., 5 3 , 3383 (1970).
The Journal of Physical Chemistry, Vol. 76, No. I,1971
NOTES
286 CzHs
+ NFa --+CzHsF + NFz (AH6" = -48 kcal/mol)
+ NF2 CzHsNFzt-+ 2HF' + CYH&N (AHBO = -148
C2H,
(5)
--j
kcal/mol)
(6)
CzHb3- F --+ C2H,Ft --3 HF' 4- CzH4
(AH,' = -97 kcal/mol)
(7)
Reaction 5 cannot produce HF, since its exothermicity is lower than the energy barrier of HF elimination from C2HsF. Nevertheless, it may be a very efficient path for removing the CzHs radical formed from reaction 4. Reactions 6 and 7 have the potential of providing vibrationally excited HF; however, their importance in comparison with reaction 4 cannot be determined in the present work. Further study, using NzF4 as a fluorine source in a flash tube, is underway. The pressure effects of CZH6 and He are plotted in Figure 2, He ma)rkedly enhances the total emission intensity, in contrast to its negative effect on the NFaH a system. It is interesting to note that the introduction of a small amount of He eliminated completely the 1
P--
c
1
I
The presence of the strong 1 40 transitions in the NFa-CaHa system offers a promising future applicstion: the direct excitation of H F molecules from the ground state for vibrational energy transfer studies, especially in view of the faot that a very simple method of producing a short higb-power chemical laser pulse is available. l2
Acknowledgment. This work was sponsored by the Advanced Research Projects Agency, ARPA Order No. 660, and by ONR under contracts RO-001-01 and RR-002-09-41; it is gratefully acknowledged. The author also thanks Drs. S. H. Bauer and G. Wolga for the use of their equipment. (13) K.L.Kompa, J. H. Parker, and G. C. Pimentel, J. Chem, Phys., 49, 4257 (1968).
New Absorption Bands in Solutions of Alkali Metals in Amines
by G,Gabor and K. Bar-Eli* Inetitute of Chemistry, Tel-Aviv University, Tel-Aviv, Israel (Received April 6 , 1070) Publication costs borne oompletely by The Journal of Physical Chemistry
3
T E c n
!
H
0
2
4
6
8
IO
P(torr ) and H e on the total HF laser Figure 2, The effect of intensity: 0 , PNW = 0.20 Torr, P Q H ~ = 2.00 Torr; PNn = 0.29 Torr, Pae = 0.
+,
1--t 0 transitions, although the overall laser output was increased by a factor of 3 as shown in Figure 2. No transitions additional to those six Pzl lines listed in Table I1 were observed when He was added. It is to be noted that, in an electrical discharge system, inert gases cannot only tra,asfer the vibrational and rotational energies from the lasing molecules but also change the characteristics of discharge. Accordingly, it is more difficult to interpret the observed effects. I n a flashphotolytic study of the UF~-HZsystem, Kompa, et U Z . , * ~ have investigated the effects of some gases (SF6, GFB, and He), which were found, mainly, to moderate the temperature rise and reduce the number of transitions observed. The Journal of Physical chemistry, Vol. 76, No. %.?# 1971
Optical absorption spectra of solutions of potassium in mixtures of methyl- and ethylamines have been studied It was shown that they have essentially two absorption bands : in the visible region (V band), A,, 890 nm, 1400-1600 nm. and in the near-ir region (ir band), A, These results are obtained provided one is careful to work in quartz vessels to avoid sodium contamination, which causes the appearance of absorption at 6SO nmV4 The ratio ir/V increases with the methylamine fraction of the mixture. On cooling a relatively dilute solution (ODv (f20') < 1.5), one observes two effects. (a) One effect is a blue shift of the V peak maxima of =-lo cm-1/deg.2*6i6 As seen in Figure 1, this shift depends on the molar ratio of the solvents, being -8.3, -10, and -11.9 cm-I/deg for X,, = 0.0, 0.509, and 1.0, respectively. [X,, and X,, denote molar fractions of methylamine and ethylamine, respectively, in a mixture of these solvents.] These results are in complete (1) H. Blades and J. W. Hodgins, Can. J. Chem., 33, 411 (1955). (2) M. Ottolenhi, K.Bar-Eli, and H. Linschits, J. Chem. Phys., 43, 206 (1965). (3) J. L. Dye and R. R. Dewald, J. Phys. Chem., 68, 135 (1964). (4) I. Hurley, T. R. Tuttle, Jr., and S. Golden, J. Chem. Phys., 48, 2818 (1968). (5! M. Ottolenghi, K. Bar-Eli, H. Linschitz, and T. R. Tuttle, Jr., %bzd., 40,3729 (1964). (6) 8. Matalon, 8. Golden, and M. Ottlenghi, J . Phvs. Chem., 73, 3098 (1969).
