J. Phys. Chem. 1984, 88, 3038-3042
3038
observed in the adsorption of benzene. This also indicates that phenylene chain length in the adsorbed biphenyl is shorter. This may be caused from the limitation imposed on the adsorbed amount of biphenyl or terphenyl, being less than that of benzene, due to the geometrical restriction of the interlayer of the clay mineral. Raman spectrum of biphenyl adsorbed on Cu2+-montmorillonite at room temperature in a dry atmosphere and that after annealing at 100 O C are shown in Figure 7. Spectrum 1 was measured by 457.9-nm excitation, while spectrum 2 was measured by 514.5-nm excitation. Notably, the latter spectrum coincides well with that of type I1 benzene species. Changes in the Raman spectra upon annealing are shown in Figure 8 in detail. The bands at 101 1, 787, and 1322 cm-I of the adsorbate which were selectively measured by 457.9-nm excitation at room temperature (Figure 8, spectrum 2) disappear upon annealing at 130 OC (Figure 8, spectrum 1). Therefore, the bands would be due to those of the biphenyl cation radical or the cations of its oligomers. The corresponding bands of the biphenyl anion radical are observed at 1017, 721, and 1326 ern-'.'' The Raman spectrum in Figure 7 (spectrum 2) is strictly the same as that of type I1 benzene, and no shifts are observed in their bands, which suggests that the resonance Raman spectra of these poly@-pheny1ene)s in the observed range are not sensitive to the chain length. Raman spectra of 0-,m-, and p-terphenyl adsorbed on Fe3+-montmorilloniteand annealed in vacuum at 130 O C are shown in Figure 9. The spectra are different from each other while the spectrum of adsorbed p-terphenyl is the same as that of type I1 benzene, which supports the mechanism that terphenyls para polymerize regularly at terminal benzene rings. In summary, benzene and phenylene molecules are observed to be polymerized to poly@-phenylene) cations in the interlayer of transition-metal ion-exchanged montmorillonites under the mild reaction conditions. These poly@-phenylene) cations are reduced in the presence of water vapor to poly@-phenylene) molecules accompanied by the reoxidation of metal ions. Registry No. Cu, 7440-50-8; Fe, 7439-89-6; Ru, 7440-18-8; Pd, 7440-05-3;C6H6, 7 1-43-2;biphenyl, 92-52-4;p-terphenyl, 92-94-4; oterphenyl, 84-15-1;m-terphenyl, 92-06-8;poly@-phenylene),25 190-62-9.
pTerphenyl
'
JV
1500
1000
500
o-Terphenyl
cm
-1
wave number cm-' Figure 9. Resonance Raman spectra of p - , 0-,and m-terphenyls adsorbed
and annealed under vacuum at 130 OC on Fe3+-montmorillonite (excitation by Ar 514.5-nm line). one similar to that of type I1 benzene species (Figure 6). On Fe3+-montmorillonite, the change to type I1 species proceeds considerably even at room temperature. The intensity of the band at 747 cm-I, which is attributed to the CH out of plane deformation of monosubstituted benzene, is weakened after the annealing but still remains, whereas the corresponding band is not
Electron Spin Resonance and Dielectric Relaxation Studies of Pyridine-Intercalated Cd2P2S6 E. Lifshitz, A. E. Gentry, and A. H. Francis* Department of Chemistry, University of Michigan. Ann Arbor, Michigan 48109 (Received: November 1 , 1983)
The transition-metal chalcogenophosphates (M2P2S6)crystallize in a layered structure of the CdC12 type. In the layered M2P2S6structure, adjacent planes of sulfur atoms are only weakly bound by van der Waals interactions and, therefore, can accommodate guest species (I) between the layers to form intercalation compounds, M2P&(I)x. The temperature dependence of the ESR spectra of Mn2+impurity centers in the metal plane of the host lattice has been utilized to investigate structural modifications associated with the progress of the intercalation reaction with pyridine. Temperature-dependent dielectric relaxation measurements have been used to study the dynamical behavior of the pyridine intercalate in Cd2P2S6.The experimental results indicate that intercalated pyridine is weakly bonded and dynamically disordered at room temperature. ESR spectroscopy has revealed structural disorder in the host lattice resulting from intercalation with pyridine.
Introduction Transition-metal chalcogenophosphates from a series of lamellar, broad-band semiconductors with general chemical formula M2PzS6 ( M = Mn, Fe, Cd, Fe, Ni, Mg and X = S, Se). The MzP& layered structure may be viewed as the MS, structure in which one-third of the metal has been replaced by a P2 atom pair.'f2 0022-3654/84/2088-3038$01.50/0
X-ray powder patterns of intercalated M2P2S6compounds indicate a monoclinic unit cell closely related to the unit cell of the host material.I4 The a and b parameters (intraplane dimensions) (1) V. W. Klingen, R. Ott, and H. Hahn, Z . Anorg. Allg. Chem., 396,271 (1973), (2) V. W. Klingen, G. Eulenberger, and H. Hahn, Z . Anorg. ANg. Chem., 401, 97 (1973).
0 1984 American Chemical Society
Pyridine-Intercalated Cd2P&
The Journal of Physical Chemistry, Vol. 88, No. 14, 1984 3039
are essentially unaltered by intercalation, while the c parameter (interplane dimension) is substantially Raman, IR, and incoherent neutron inelastic scattering studies indicate that intercalated species interact weakly with the host lattice and are dynamically disordered at room temperature.8-10 EXAFS and magnetic susceptibility studies have shown that intercalation induces local disorder in the structural environment of the metal.11,12 It is desirable to understand the structural modifications of the host lattice which accompany intercalation and, additionally, to obtain more detailed information about the dynamical behavior of the intercalate molecule within the van der Waals gap. To this end, we have conducted a series of ESR and dielectric relaxation investigations of pyridine-intercalated Cd2P2S6lattices. In these experiments the ESR spectrum of a small concentration of paramagnetic Mn2+ions, which substitutionally replace Cd2+in the Cd2P2S6lattice, was used to follow structural changes associated with pyridine intercalation.
Experimental Section The synthesis of Mn2+-doped Cd2P2S6was accomplished by the method reported in ref 13. Intercalation was achieved by heating selected single crystals of the pure material in pyridine for 3 days in a Vycor tube sealed under vacuum. When the reaction was carried out at 80 O C , yellow crystals were obtained with the crystal morphology of the starting material well-preserved. At higher temperatures (120 "C), very fragile, deep orange crystals were obtained. The fragility and poorly defined cleavage planes of these crystals indicated that severe structural damage had occurred. All ESR and dielectric relaxation measurements were carried out on the yellow product. Chemical analysis of the orange product gave an elemental composition corresponding to an empirical formula of CdPS3(py)o,43(Cd, 41.64; P, 10.32; S, 39.66; N, 1.33; C, 6.03; H, 1.02%). This is in good agreement with thermogravimetric analyses (TGA) of the orange product ( x = 0.41). The percentage of hydrogen, however, is about twice that required by the empirical formula (0.46%)and suggests that, although dry reagents were used and the material does not appear to be hydroscopic, traces of water were present in the analyzed sample. TGA of the yellow crystals consistently gave x = 0.50 =k 0.02. Similar results were obtained from powdered samples and large single crystals. X-ray diffraction measurements of the basal spacing of the two compounds were not performed. A Bruker ER 200E-SRC spectrometer with 100-kHz field modulation and a Bruker TM,,,-mode cylindrical cavity were used to record the X-band spectra. Single-crystal samples were oriented optically and mounted on a goniometer attached to the microwave cavity. A Varian Model V-4561 spectrometer with 100 kHz modulation frequency and a TEol,-mode cylindrical cavity were used to record the Q-band spectra. The variation of the spectra with temperature was measured only for the X-band investigations. The temperature of the crystal was varied from ambient to 137 K with a Varian Model 4257 variable-temperature accessory modified to fit the Bruker microwave cavity. A second varia-
c.:; I
I
1
1
I
(3) B. E. Taylor, J. Steger, and A. Wold, J . Solid Scare Chem., 7, 461 (1973). (4) R. Brec., G. Ouvrard, A. Louisy, and J. Rouxel, Ann. Chim. (Paris), 5, 499 (1980). (5) R. Clement, J. J. Girerd, and I. Morgenstern-Badarau, Inorg. Chem., 19, 2852 (1980). (6) R. Clement, J . Chem. SOC., Chem Commun., 647 (1980). (7) K.Clement and M. L. H. Green, J . Chem. SOC.,Dalton Trans., 10, 1566 (1979).
(8) X. Mathey, R. Clement, C. Sourisseau, and G. Lucazeau, Inorg. Chem., 19, 2773 (1980). (9) C. Sourisseau, J. P. Forgerit, and Y.Mathey, J . Phys. Chem. Solids, 44, 119 (1983). (10) C. Sourisseau, Y . Mathey, and C. Poinsignon, Chem. Phys., 71, 257 I1 QR7\ ,-~--,.
(11) M. Michalowicz and R. Clement, Inorg. Chem., 21, 3872 (1982). (12) R. Clement, J. P. Andiere, and J. P. Renard, Reu. Chim. Miner., 19, 560 (1982). (13) J. Boerio-Goates, E. Lifshitz, and A. H. Francis, Inorg. Chem., 20, 3019 (1981).
(14) U. K. Jain and P. Venkateswarlu, J . Phys. C, 12, 865 (1979). (15) E. Lifshitz, and A. H. Francis, J . Phys. Chem., 86, 4714 (1982).
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The Journal of Physical Chemistry, Vol. 88, No. 14, 1984
transitions, which indicates crystalline perfection. The line width is about 12 G. Pyridine-Intercalated CdzP2S6. The X-band ESR spectrum shown in Figure l b was obtained from a room-temperature Cd2P& (1% Mn) single crystal after intercalation with pyridine. A single, broad, nearly isotropic line with g = 2.026 and a peak-to-peak width of 502 G is observed. The X-band spectrum shown in Figure I C is obtained upon cooling the sample to 250 K or below. It consists of the partially resolved six hyperfine lines of the s -‘Iz fine-structure transition, accompanied by weaker lines due to the forbidden fine-structure transitions. The hyperfine components widen monotonically toward higher field from a line width of 21.3 G (first component) to 42.7 G (sixth component). The Q-band spectrum of Mn2+doped in pyridine-intercalated CdzPzS6single crystals at ambient temperatures is shown in Figure Id. The spectrum contains six well-defined hyperfine components, each 30 G wide. The hyperfine widths remain virtually unchanged with increasing field. The line-broadening effects evident in spectra b, c, and d of figure 1 are the result of both static and dynamical disorder in the pyridine-intercalated Cd2P2S6lattice. Intercalation results in the loss of the AS/, F? f 3 / , and h3jZF? fine-structure groups whose resonant fields are extremely sensitive to orientation + *ljZfine-structure transition and the retention of the *’Iz which is, in first order, independent of orientation (provided g is not strongly anisotropic). The monotonic broadening of the + hyperfine components toward higher fields is also characteristic of structural disorder. Order of magnitude estimates of the Mn2+ ESR line widths using the spin-Hamitonian parameters reported in ref 16 indicate that the major source of line broadening is modulation of the quadratic zero-field splitting by thermally stimulated motion of the pyridine intercalate. Support for this conclusion is found in the observation that the ESR line widths are narrower at Q band than X band. The pyridine intercalate can interact with the sulfur layer, causing both a static and dynamic distortion of the M-S bonds around the central metal atom, or may coordinate directly with the metal, introducing a strong anisotropy into the local metal environment. The line-broadening effect is similar to that observed in an ESR study of the complex formed between Mn(Hz0)62+ and pyridine in aqueous solution by McGarvey.I7 The ESR line broadening was shown to result from the complex-induced anisotropy of the metal environment. The effect of decreasing the symmetry about [Mn(Hz0)6]z+was marked, the resonance literally disappearing when a complexing pyridine group was added. The dynamical behavior of the pyridine intercalate above 250 K introduces additional homogeneous line broadening through modulation of the zero-field splitting (ZFS). Accordingly, at high temperatures, the line shape will depend on the correlation time of the pyridine motion. Modulation of the ZFS by both rotational and collisional motions of pyridine molecules in the proximity of the paramagnetic center must be separately considered. Unfortunately, the theory for homogeneous line broadening by temporal modulation of the ZFS has been developed only for a paramagnetic center tumbling in a static environment. However, the final form of the theoretical expression for the line width is not expected to be substantially different for the three cases, and it is believed that the relaxation parameters obtained from the existing theory will be of the correct magnitude. The experimental temperature dependence of the line width may be analyzed in terms of an “average line width”, ( l/Tz), introduced by McLachlan for the case S = 5/z. The appropriate expression for the temperature-dependent line width is’* ( l / T z ) = [64/100][3
+ 5/(1 + w2r:) + 2/(1 + w 2 r 2 ) ] A 2 ~ (1)
(16) E. Lifshitz, Ph.D. Thesis, University of Michigan, 1983. (17) B. R. McGarvey, J . Phys. Chem., 61, 1232 (1957). (18) A. D. McLachlan, Proc. R. SOC.London, Ser. A , 280, 271 (1964).
Lifshitz et al. Here, AZ is the trace of the square of the ZFS tensor Az = z/3Dz 2E2, w is the Larmor frequency of the electron, and r, is the correlation time associated with the modulation of the ZFS. The expression is valid only for the range of fast motion where wr, I1. The temperature dependence of the line width arises from the thermally activated motion of the pyridine intercalate described by
+
r, = A-’ exp(AE/kT)
where AE is the activation energy for the motion and A is the usual preexponential frequency factor. Equations 1 and 2 predict an exponential dependence of the experimental line width on temperature. Therefore, the activation energy for pyridine motion may be estimated from the slope of a plot of In (l/Tz) vs. 1/T. For this purpose, the line widths of individual hyperfine lines within the +‘I2 e fine-structure group were used, and the value obtained for the activation energy was -1083 cm-’. Because of the rapid coalescence of the hyperfine structure with increasing temperature, there is considerable uncertainty in the determination of the activation energy (-50%). In order to determine the correlation time of the pyridine motion in CdzP2S6, the procedure introduced by Levanon et al. was adopted.I9 The ratio of the peak-to-peak line widths at room temperature of the X-band and Q-band spectra was computed from the experimental data. The experimental value of the ratio was then compared with the theoretical value as a function of correlation time reported by Levanon et The theoretical values were obtained from consideration of the Redfield relaxation matrix for S = 5/z, assuming a tumbling motion of the paramagnetic centers. The correlation time was found to be 8 X s at room temperature. This is about 1 order of magnitude larger than the rotational period of pyridine in the liquid but is the correct magnitude for the collisional frequency of pyridine with interior crystal surfaces. The value obtained for T , is considerably larger than that for s).” In a the [ M I I ( H ~ O ) ~ ]ion ~ ’ in aqueous solution solution T, is determined by the combined effect of the tumbling period of the hydrated ion and the mean time between water molecule collisions with the hydrated ion shell. Evidently, in the restricted environment of the van der Waals gap, line broadening is caused principally by collisions of the intercalated pyridine with the exposed faces of the MnS6 octahedra. The dynamical motion of intercalates in the van der Waals gap of M2P2S6compounds at room temperature has been studied previously. Raman and IR studies of Co(Cp), and Cr(Cp), intercalated into MnPS3, ZnPS3, and CdPS3 showed that these intercalates interact weakly with the host lattice and are dynamically disordered at room t e m p e r a t ~ r e . ~Incoherent ,~ inelastic neutron scattering of Mn2PzS6[Co(Cp)z], indicated rotational jumps of the rings of the intercalate with a correlation time equal to about s at room temperature.I0 Similar dynamics of the CoCp, intercalate in TaSz have been suggested by NMR studies.23 When the intercalated lattice is heated above 470 K, additional hyperfine structure associated with the k 5 j 2s k 3 I 2and k 3 / , F? fine-structure transitions reappears. TGA measurements indicate that pyridine deintercalates between 385 and 670 K. Figure Id is the ESR spectrum obtained after heating to 670 K and recooling to room temperature. Although the 30-line spectrum typical of Mn2+is regained, the hyperfine line width is considerably broader than that observed prior to intercalation (Figure la). There remains, therefore, some residual static disorder in the Cd2P2S6lattice subsequent to deintercalation. It appears likely that the remaining static disorder is due to the formation of residue compounds during the deintercalation process. The detailed structure of these compounds is not known, but formation of the (19) H. Levanon, G. Stein, and Z. Luz, J . Chem. Phys., 53, 876 (1970). (20) M. Rubinstein, A. Bararn, and Z. Luz, Mol. Phys., 20, 67 (1971). (21) N. N. Tikhomirova, I. V. Nikolaeva, V. V. Demkin, E. N. Rosolovskaya, and K. V. Topchieva, J . Cutal., 29, 105 (1973). (22) B. G. Silbernagel, Chem. Phys. Lett., 34, 298 (1975). (23) M. S. Dresselhaus, and G. Dresselhaus, Adv. Phys., 30, 139 (1981).
The Journal of Physical Chemistry, Vol. 88, No. 14, 1984 3041
Pyridine-Intercalated Cd2P2S6
T (K) 400.
350.
300.
250.
d j
LT
0.32
0.24
l/T
0.40
(.lo2)
Figure 3. Plot of In (tan 6) vs. 1 / T for pyridine-intercalated Cd2P2S6.
laxation time. The ratio of the real to the imaginary term gives the loss tangent tan 6. In the low-temperature limit tan 6
2 2 00
100
300
4 00
Temperature (K)
Figure 2. The temperature dependence of the capacitance and loss tangent of Cd2P,S6(dashed line) and the pyridine-intercalated lattice (solid line).
residue compounds upon deintercalation is common in layered compounds. In particular, they have been studied in graphite, where the stacking arrangement of deintercalated graphite does not regain completely its original arrange men^^^ The static distortion of the metalsulfur bonds in Mn2P2S6upon intercalation with cobaltocene has been confirmed by EXAFS studies.’ The bond-length root-mean-square standard deviation induced by intercalation lies in the range 0.05-0.07 A for the Mn-S distances and 0.1-0.15 A for the Mn-Mn and Mn-P distances. An approximate correlation between the fine-structure parameter D and the metal-ligand bond length may be obtained from the study of Mn2+ESR in other M2P2S6lattices.16 We have studied previously the series M = Zn, Cd, and Mg and have correlated D with the metal ion radius. These results suggest that a 0.1 5 8,variation in the Mn-S distance would produce variations of about 30-40% in the D parameter. Calculations indicate that variations of this magnitude in the parameters of the spin Hamiltonian do lead to significant line broadening but do not result in the loss of the fine-structure transitions. @ 3/2 or 3/2 @ Therefore, in the absence of dynamical disorder effects, a poorly resolved, 30-line, ESR spectrum is expected. Dielectric Relaxation. The dipole amount of pyridine is large (2.2 D) and may be expected to contribute substantially to the complex dielectric constant of the intercalated Cd2P2S6lattice. The temperature dependence of the dielectric constant, therefore, provides a sensitive determination of the onset of pyridine motion in the lattice. The dielectric constant of a material has both real (e’) and imaginary (e”) terms. The frequency response of the complex dielectric constant, Z = e’ ie”, is given by the Debye equations.24 In the low-temperature limit (UT >> l ) , these equations yield
+
€’(U,T) N C”(W,T)
€,(e,
(e,
- €,)/(W2T2)
(3)
- €,)/(UT)
(4)
where t, and em are the real static and infinite-frequency values of the dielectric constant. T is the characteristic dielectric re(24) v. v. Daniel, “Dielectric Relaxation“, Academic Press, New York,
1967.
E
(es/em - ~ ) / ( w T )
(5)
If T is assumed to have the form given by eq 2, the relative capacitance and tan 6 both increase exponentially with temperature when W T >> 1. The temperature dependence of the relative capacitance of both cd2P2S6and Cd2P2S6(py)is shown in Figure 2. The measured capacitance includes contributions from the host lattice as well as lead capacitance. The dramatic increase in the capacitance of the intercalated sample relative to that of the host lattice from 250 to 400 K is due to the reorientational contribution of the pyridine dipoles to the dielectric constant. Measurements were made with the bridge voltage ( E ) parallel to the stacking axis (c*); therefore, only reorientational motion which changes the projection of the pyridine dipole on c* contributes to the experimental value of the dielectric constant at low frequencies. Rotation about C, can not be detected in the dielectric relaxation experiment in first-order effects. If the pyridine equilibrium orientation is other than coplanar with the lamellae, then motion about either axis perpendicular to C, would contribute to the dielectric constant. Assuming T to be of the form given in eq 2, we may obtain the activation energy from the slope of a plot of In (tan 6) vs. 1/T. This plot is shown in Figure 3 and yields a slope, from the linear region, of 3240 cm-’. The deviation from linearity at high temperatures is associated with deintercalation of pyridine from the host lattice.25 This is of the same magnitude, but higher, than the activation energy for pyridine motion determined from the ESR line broadening. We note that that motion which leads to broadening in the ESR spectrum is not necessarily the same as that measured in the dielectric relaxation experiment. For example, it is possible that ESR line broadening is sensitive to rotation about C2,whereas the dielectric constant, in first order, is not.
Summary The temperature dependence of the ESR spectrum of paramagnetic Mn2+centers in Cd2PzS6(py)has been used to investigate the static and dynamical behavior of the pyridine intercalate. Line-broadening effects indicate that the pyridine introduces irreversible static structural disorder into the host lattice. Additionally, the pyridine intercalate is dynamically disordered at room temperature. ESR measurements yield an activation energy of -1083 cm-’ for pyridine motion correlated with ESR line broadening. The correlation time determined for the thermal motion of pyridine within the van der Waals gap a t room temperature is ( 2 5 ) A. E. Gentry, Ph.D. Thesis, University of Michigan, 1983.
3042
J . Phys. Chem. 1984, 88, 3042-3047
8 X 10-l2s, which is about an order of magnitude too large for rotational motion but approximately the value expected for collisional motion with the exposed faces of the CdS6 octahedra. The temperature dependence of the dielectric constant of pyridine-intercalated Cd2P2S6has been used to investigate the
dynamical behavior of the pyridine intercalate. The activation energy for pyridine motion was determined to be 3240 crn-l. The motion is associated with changes in the direction of the pyridine dipole moment perpendicular to the Cd2P2S6stacking axis and is not necessarily that observed in the ESR experiment.
The Photochemistry of Argon Matrices Containing Nitric Oxide and Carbonyl Sulfide. 2. The Photoproducts SNO and SN,O," Michael HawkinsIb and Anthony J. Downs* Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, England (Received: October 24, 1983)
The reaction of sulfur atoms, generated by ultraviolet photolysis of carbonyl sulfide, with monomeric and dimeric nitric oxide isolated in argon matrices at 13-20 K leads to the formation of products with the molecular formulas SNO and SN202. Assignments based on the infrared spectra of the three isotopomersS14N160,Sl5NI60,and S14N1s0place the N-0 stretching and N-S stretching fundamentals of SI4Nl6Oat 1554.9 and 790.0 cm-I, respectively, after allowance for Fermi resonance between uNo and 2vNS. The third fundamental, the bending mode, could not be detected with certainty but is estimated to occur at ca. 567 cm-'. SN,02 appears to exist in two isomeric forms, probably S(O)N.NO and ONSNO, the reversible interconversion of which is promoted by photolysis: S(O)N.NO P ONSNO. Three vibrational fundamentals of each isomer and S5N202. have been identified for the two isotopomers SJ4Nz02
Introduction Although there is a wealth of information about the nitrogen oxide molecules N O , (x = 1-3) and N20y0,= 1-5), few of the analogous (acyclic) nitrogen sulfides are known with any certainty. It is true that the gaseous thiazyl radical, N S , has been characterized by its m i c r o w a ~ evisible , ~ ~ ~ emission,2 electron spin resonance,2 photoelectron,4 and high-resolution infrared5 spectra, but no more than tentative claims touch upon the identification of nitrogen disulfide, NS2,6and dinitrogen sulfide, N2S.7 Mixed oxide sulfides of nitrogen like SNO or SN202have fared no better. Tchir and Spratley have reported that two infrared absorptions attributable to nitrogen oxide sulfide, SNO, develop after ultraviolet irradiation of argon matrices containing cis-thionyl imide, "SO.* A single infrared absorption which appeared after vacuum-UV irradiation of matrix-isolated cis-"SO has also been ascribed by the same workers to a second isomer, viz. N S 0 . 9 Evidence for the formation of a species with the molecular formula SNO has also been derived from two studies involving the flash photolysis of gaseous carbonyl sulfide in the presence of nitric oxide. The firstlo revealed a visible emission in the region 350-430 nm exhibiting complex vibrational fine structure, although no attempt was made to identify its source. The second" established (1) (a) Presented in part at the 3rd International Meeting oh Matrix Isolation, Nottingham, England, July 1981. When our investigations were already well advanced, we learned of an independent matrix-isolation study of the photochemically induced interaction of OCS with NO, this was reported by: Fredin, L.; Pimentel, G. C. "Abstracts of Papers", 178th National Meeting of the American Chemical Society, Washington, D.C., Sept 1979; American Chemical Society: Washington, D.C , 1979; PHYS 191. (b) Present address: Sevenoaks School, Sevenoaks, Kent TN13 lHU, U.K. (2) fIeal, H. G. Adu. Inorg. Chem. Radiochem. 1972,15, 375 and references cited therein. (3) Lovas, F. J.; Suenram, R. D J . Mol. Spectrosc. 1982, 93, 416. (4) Dyke, J. M.; Morris, A.; Trickle, I. R. J. Chem. SOC.,Faraday Trans. 2 1977, 73, 147. ( 5 ) Matsumura, K.; Kawaguchi, K.; Nagai, K.; Yamada, C.; Hirota, E. J . Mol. Spectrosc. 1980, 84, 68. (6) Pannetier, G.; Dessaux, 0.; Arditi, I.; Goudmand, P. C. R . Hebd. Seances Acad. Sci. 1964, 259, 2198. (7) Powell, F. X. Chem. Phys. Lett. 1975, 33, 393. (8) Tchir, P. 0.;Spratley, R. D. Can. J . Chem. 1975, 53, 2318. (9) Tchir, P. 0.;Spratley, R. D. Can. J. Chem. 1975, 53, 2331. (10) Basco, N.; Pearson, A. E. Trans. Faraday SOC.1967, 63, 2684. (1 1) Van Roodselaar, A.; Obi, K.; Strausz, 0.P. Int. J. Chem. Kinet. 1978, 10, 31.
0022-3654/84/2088-3042$01.50/0
that sulfur atoms decay at a rate which can be rationalized in terms of the formation of a complex with the composition SNO. Encouraged by the capacity of matrix-isolation methods to bring to light species short-lived under normal conditions, we have investigated the reactions which take place in solid argon matrices between sulfur atoms and either monomeric nitric oxide or the dimer cis-N,02. This paper describes the infrared spectra of the matrices which bear witness to the formation of the molecules SNO and S N , 0 2 ; it also presents evidence that SN202,like NZ03,12 exists in different isomeric forms which are susceptible to photochemical interconversion.
Experimental Section Apparatus. Matrices were deposited on a CsI window cooled to 13-20 K by means of a Displex refrigerator (Air Products, Model CS 202). Temperatures were measured with a chrome1 vs. iron-doped gold thermocouple or with a hydrogen-vapor bulb and were varied by adjusting the voltage applied to a 20-W heater wound around the second stage of the refrigerator. Surrounding the cold station of the refrigerator was a shroud which was evacuated to a pressure less than torr. Infrared spectra were recorded with either a Perkin-Elmer Model 225 or a Perkin-Elmer Model 580 spectrophotometer. With the internal calibration available on the Model 580 instrument, wavenumbers were reproducible to better than 0.4 cm-I, and the resolution was invariably better than 0.5 cm-' in measurements involving precise wavenumber determination. Sample photolysis was effected with either a Philips HPK 125-W medium-pressure mercury arc or a Philips 070 T 25-W cadmium arc. A 2- or 4-cm water filter reduced the amount of infrared radiation incident upon the matrix when the mercury arc was in use, and a Balzer absorption filter served, where necessary, to remove UV light with wavelengths shorter than 375 nm. Whereas the primary UV emission of a mercury arc is in the region of 254 nm, that of the cadmium arc is at 228 nm.I3 Chemicals. Argon (grade "X", 99.995%) was used as received from the British Oxygen Co. Carbonyl sulfide and nitric oxide, (12) Varetti, E. L.; Pimentel, G. C. J . Chem. Phys. 1971, 55, 3813. (13) Meggers, W. F.; Corliss, C. H.; Scribner, B. F. "Tables of Spectral-Line Intensities, Part I", 2nd ed.; National Bureau of Standards, Monograph 145: Washington, D.C., 1975.
0 1984 American Chemical Society
