Raman Spectrum of Thionyl BromideH. Stammreich, Roberto Forneris, and Yara Tavares Citation: The Journal of Chemical Physics 25, 1277 (1956); doi: 10.1063/1.1743194 View online: http://dx.doi.org/10.1063/1.1743194 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/25/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Raman Spectrum of Polycrystalline Methyl Bromide J. Chem. Phys. 41, 2842 (1964); 10.1063/1.1726362 Raman Spectra of Thionyl Fluoride and Sulfuryl Fluoride J. Chem. Phys. 23, 1316 (1955); 10.1063/1.1742267 Microwave Spectrum of Ethyl Bromide J. Chem. Phys. 23, 599 (1955); 10.1063/1.1742052 Depolarization Ratios of the Raman Bands of Thionyl Chloride J. Chem. Phys. 23, 209 (1955); 10.1063/1.1740537 Raman Spectrum of Aluminum Bromide J. Chem. Phys. 8, 643 (1940); 10.1063/1.1750733

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LETTERS TO THE EDITOR 1277

only asymptotically (infinite Lagrangian time) from above. Co is never reached; even if the state point were to pass B, it would be forced back since properties of the equation of state similar to those leading to Jouguet's rule will result in r changing sign when E is crossed.

Since at large distances behind the wave front, the mass velocity approaches UB, directed toward the unreacted explosive, we conclude that the solution proposed is not a "free" wave, but is instead an everywhere-steady driven wave supported by a piston moving with velocity UB. Since the wave corresponding to OCoA was the only possible solution of the von Neumann type, we conclude that such solutions do not exist for the present case. Steady-state conditions in the reaction zone, strictly speaking, can only be approached asymptotically. The theory in its present form does not describe this asymptotic state. The steady-state theory, to date the only feasible analytical approach, leads only to a one parametric family of everywhere-steady piston supported flows, the one of minimum propagation velocity and piston ve­locity having as final state the "equilibrium CJ point" C. It should be mentioned that von Neumann2 considered only the case of an irreversible reaction going to completion, in which case the distinction between Co and c, Co, and C disappears.

Our discussion does not apply to the case of more than one reaction process, which is presently under consideration.

* Work performed under the auspices of the U. S. Atomic Energy Commission.

1 J. G. Kirkwood and W. W. Wood. J. Chem. Phys. 22,1915-1919 (1954). 2 J. von Neumann, OSRD-549 (1942). 3 Y. B. Zeldovitch, J. Exptl. Theoret. Phys. (USSR) 10,542 (1940). • S. R. Brinkley, Jr .. and J. M. Richardson, Fourth Symposium (Inter­

national) on Combustion (Williams and Wilkins, Baltimore, 1953), p. 450.

5 R. Courant and K. O. Friedrichs, SuPersonic Flow and Shock Waves (Interscience Publishers, Inc., New York), p. 204.

6 W. Fickett (private communication).

Electronic Structure of s Tetrazine LEONELLO PAOLONI

Laboratorio di Chimica Terapeutica, Istiluto Superiore di SanitiJ, Ramo (Received October 15, 1956)

T HE semiempirical theory of electronic spectra proposed by Pariser and Parrl has met with considerable success not only

when applied to unsaturated hydrocarbons but also in the case of conjugated N-heterocyclic molecules. But as far we know no treatment has yet been reported of molecules having two adjacent nitrogen atoms. When recently internuclear distances and bond angles of s tetrazine became available2 we thought it interesting to see whether the Pariser and Parr method could account for its observed spectrum} This implies the choice of a suitable value for the resonance integral fJNN, which might then be used in the study of other molecules, also for ascertaining to what extent the semiempirical procedure allows reliable results.

s Tetrazine (I) is a planar molecule, whose hexagonal benzene­like ring makes the benzene MO's the most convenient starting eigenfunctions. Our treatment follows therefore that outlined by Pariser and Parr.l Changes have been made (i) in the choice of (pp I pp) integrals, which were obtained through the empirical relationship (pplpp)=3.29.Z p ev, discussed in a recent paper4; (ii) in the evaluation of the (pp I qq) integrals, for which theoretical values were used" on distances ;:: 2.8 A; (iii) in the penetration integrals, which were all neglected. Results are collected in Table 1. They are obtained with the fJON value - 2. 74 ev deduced" from the observed spectrum of s triazine and previously used for melamine,1 and with a fJNN = - 2.35 ev, chosen to fit the observed spectrum of s tetrazine. Here3 the weak band at about 520 mIL is considered as ,,--n, while the strong band with peak at 252.5 mIL (4.91 ev) is regarded as due to the first singlet-singlet, "--"-, transition. The second calculated transition, IB2u;--1A lv, is ex­pected near 210 mIL and less intense than the first one, whereas the singlet-triplet transitions at 325 to 350 mIL fall in a region which is

TABLE I. Calculated excited energy levels of s tetrazine.

Energy Oscillator State (ev) strength

IBsu 4.91 0.103 IB2u 5.85 0.019 3B3u 3.60 0 SB2u 3.89 0

given as nearly transparent in the published spectrum3; lack of experimental data prevents therefore a further check of the present results.

Work is now well advanced in which 3,6-diamino-l,2,4,5-tetrazine, described by Lin et al.,s is treated according to the procedure previously followed for melamine. 7 The fJNN integral here found will be used, so that no new empirical parameters need to be introduced in the calculations. The results will be published in full elsewhere.

H C

/"'­N N I II N N '\./

C I H

1 R. Pariser and R. G. Parr, J. Chem. Phys. 21, 466, 767 (1953) . 2 Bertinotti, Giacomello, and Liquori, Acta Cryst. 9, 510 (1956). 3 A. M. Liquori and A. Vaciago, Ricerca sci. 26, 181 (1956). ·L. Paoloni, Nuovo cimento X, 4, 410 (1956). 'R. Pariser, J. Chem. Phys. 24, 250 (1956). • Hirt, Halverson, and Schmitt, J. Chem. Phys. 22, 1148 (1954). 7 M. J. S. Dewar and L. Paoloni, Trans. Faraday Soc. (to be published). S Lin. Lieber, and Horwitz, J. Am. Chem. Soc. 76, 427 (1954).

Raman Spectrum of Thionyl Bromide* H. STAMMREICH, ROBERTO FORNERIS, AND YARA TAVARES

Department of Physics, Faculty of Philosophy, Science and Letters, University of Slio Paulo, Slio Paulo, Brazil

(Received October 2, 1956)

T HIS note reports the complete Raman spectrum of SOBr2 with an assignment of the observed frequencies. No spec­

tral data regarding this molecule were found in the literature; however the spectra of the similar oxyhalides SOF 2, SOCI2, and SeOCI. have been investigated. Electron diffraction data on SOCI. and SOBr2 support strongly a pyramidal structure of these molecules' possessing but one element of symmetry, namely, a plane containing the sulfur and the oxygen nucleus normal to the SCI. or SBr2 plane. The resulting symmetry belongs to the C. point group, and therefore we have to expect a Raman spec­trum showing four polarized shifts (vibrations of typeA'),and two depolarized shifts (of type A"). The planar structure of symmetry C2v formerly assumed by a number of authors should have three vibrations of class A I (polarized), two of class B I , and one of class B2 (the last three depolarized). More recent Raman' and infrared3 data on the SOCI. molecule agree better with the assump­tion of the C. symmetry.

Thionyl bromide was prepared as described by Mayes and Partington,4 passing a slow stream of HBr through freshly dis­tilled SOCh for twelve hours. The crude product was directly distilled into the Raman tube at 1 mm pressure. SOBr, decom­poses slowly giving off bromine, sulfur monobromide, and sulfur dioxide, changing its original yellow color into deep red.

Due to the darkening of the sample we excited the Raman spectra by the helium radiations 6678 A and 7065 A employing our usual technique." The spectra were recorded on hypersensitized Kodak IN spectroscopic plates; we needed exposure times from one to five hours, and up to ten hours for qualitative polarization

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1278 LETTERS TO THE EDITOR

measurements. The spectra of older samples showed the Raman frequency of bromine; shifts belonging to the other decomposition products were not observed.

Table I lists the observed frequencies, the estimated intensities, and the state of polarization, together with our assignment.

Regarding the assignment we followed the notation of Martz and Lagemann3 for SOC!., considering the state of polarization of the observed frequencies, their values and relative intensities, as compared with those of thionyl chloride, and the approximate character of the involved motions. P" Po, and P2 correspond essen­tially to the bending, asymmetric stretching, and symmetric stretching modes of vibration of the SBr2 group; it is to be noted

TABLE I.

Vibration Class Observed frequencies

v. A' 120 (lO.P) vo A" 223 (7.dp) V3 A' 267 (IO.P) v, A" 379 (5.dp) v, A' 405 (7.P) VI A' 1121 (2,p)

that, as in SOC!', the highest of these three frequencies has to be ascribed to the in-phase stretch of the SBr2 group, since Po corre­sponds to a depolarized Raman shift and represents therefore the asymmetric stretching motion. VI is doubtless the stretching vibra­tion of the S = 0 group; P6 and P, correspond to torsional and deformation modes of vibration, respectively, involving motions of all atoms of the molecule, the former one being asymmetric with regard to the plane of symmetry.

We attempted to obtain the Raman spectrum of selenium oxy­bromide in a similar manner, but the compound, relatively stable in the solid state, decomposes very rapidly in solutions, and the complete spectrum could not be registered.

* Work supported by the Conselho Nacional de Pesquizas, Rio de Janeiro; the authors wish to express their acknowledgment for the facilities created by the C.N .Pq.

1 D. P. Stevenson and R. A. Cooley, J. Am. Chern. Soc. 62, 2477 (1940). • Gerding, Smit, and Westrik, Rec. trav. chim. 60, 513 (1941); R. Vogel­

Hogler, Acta Phys. Austriaca I, 323 (1948); C. A. McDowell, Trans. Faraday Soc. 49, 371 (1953).

• D. E. Martz and R. T. Lagernann, J. Chern. Phys. 22, 1193 (1954). • H. A. Mayes and J. R. Partington, J. Chern. Soc., 1926,2594. 'H. Stammreich, Spectrochirn. Acta 8, 41 (1956).

Raman Spectra and Force Constants of GeI4 and SnI4*

H. STAMMREICH, ROBERTO FORNERIS, AND YARA TAVARES

Department of Physics, Faculty of Philosophy, Science and Letters, University of Sao Paulo, Sao Paulo, Brazil

(Received October 2, 1956)

T HE tetraiodides of germanium and tin are regular tetra­hedral molecules as shown by electron diffraction measure­

ments! and have therefore a symmetry belonging to point group Td • The nine fundamental vibrations of a pentatomic molecule with this symmetry correspond to four distinct frequencies: a totally symmetric one of class AI(PI), a doubly degenerated one of class E (P2), and two triply degenerated ones of class F2 (v"v,); all of them are to be expected Raman active, with VI polarized.

The present note reports the complete Raman spectra of the two mentioned molecules, the assignment, and the force constants calculated from the observed frequencies.

The vibrational spectrum of Snl, is incompletely known; the breathing frequency PI was observed by Delwaulle, Buisset, and Delhaye2 in the Raman spectrum of mixtures of SnCl" Snl" and the different chloroiodides, and another one (va) by Hooge3 in a "simultaneous transition" spectrum of a mixture of Snl, and CS2. The complete Raman spectrum of Gel, was reported by Delwaulle,' but since this spectrum was seemingly obtained from

a mixture with GeCl, and the whole series of chloroiodides of Ge, and without polarization measurements, we thought it worth­while to investigate the pure substance. Our results are in good agreement with the values reported by Delwaulle.

The two compounds were prepared as described in the chemical literature: Gel, by the action of freshly distilled hydriodic acid on Ge02, and Snl, by direct combination of the elements in

Gel. Observed

As-sign- Del-ment Class waullea.

v, E 56 v. F, 83 VI Al 155 PI F, 263

a See reference 4. b See reference 2. c See reference 3.

This work

60 (lO,dp) 80 (lO,dp)

159 (8,P) 264 (2,dP)

TABLE I.

Snl. Observed

Cal- Delwaulle Cal-cu- et al. b (R.) cu-

lated Hooge' (S.T.) This work lated

60 47 (lO,dp) 47 79 63 (lO,dp) 62

159 153 (R.) 149 (S,p) 149 264 221 (S.T.) 216 (2,dP) 216

CS'; both were purified by recrystallization from solutions in organic solvents. The spectra were taken using 0.5 molar solu­tions in CS'; Snl, was also investigated in a 0.13 molar solution in CCl,.

The Raman spectra were excited by He 5876 A and photo­graphed on Kodak Super Panchro Press plates, and by He 6678 A, using Kodak spectroscopic plates 103 aF for registering. The optical arrangement was the same used recently by the authors for the investigation of the Raman spectra of PI, and AsI, 0; the required exposure times were much shorter in the present case, due to the high intensity of the Raman scattering of the tetra­hedral molecules, and ranged from 5 to 30 min; exposures up to 2 hr were needed for qualitative polarization measurements.

Molecule

Gel. Snl.

Kxy

1.414 1.351

TABLE II.

Force constants in dynes cm-1 105

K" Kxx K.

0.047 0.117 -0.009 0.026 0.075 -0.010

Table I lists our observed Raman shifts, the estimated intensi­ties, and the state of polarization to be compared with the values previously reported by the above-mentioned authors.

The force field of this type of molecules has been studied by a large number of authors. Besides the simple valence force model (with two force constants), and the central force model (with three potential constants), more general potential functions have been proposed in order to fit the observed frequencies better than these simple models. The most general function is due to Rosen­thal,6 and contains five force constants, but its application depends on the possibility to establish a further relation between at least two of them, since we have only four distinct frequencies at our disposal for the solution of the resulting equations. Among others, work in this direction has been done by Urey and Bradley,' Wu,' Simanouti,· and Heath and Linnett.lO It seems that the last authors' model, assuming an orbital valence force field (OVFF) with the addition of a repulsion field between the non bonded atoms, agrees best with the observed frequencies of a large number of regular tetrahedral pentatomic molecules, but the calculation of the constants of the potential function is rather tedious.

We have attempted to calculate the force constants of the two tetraiodides from the observed fundamentals, applying the methods quoted above and have obtained the best fit using the model of Wu' which combines central and valence forces. Table II shows the four force constants for Gel, and Snl,; the numerical

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