Matrix reactions of dichlorodisulfane with alkali metals

JOURNAL

OF MOLECULAR

Matrix Blue

SPECTROSCOPY

Reactions

Absorption

72, 342-348 (1978)

of Dichlorodisulfane

Spectrum

of the

S&I

Radical

with Alkali in Solid

Argon

Metals at 20 K

CHARLES A. WIGHT’AND LESTER ANDREWS Chemistry Department, University of Virginia, Charlottesville, Virginia 22901 Matrix reactions of alkali metal atoms and SzC& produced a new absorption from 382 to 456 nm with 470 to 490 cm-i vibrational spacings. This spectrum, also produced by mercury arc photolysis of an Ar/S2C12 = 200/l sample during deposition, is assigned to the SK1 radical. Photolysis of Ar/OCS = 400/l samples during deposition produced the strong, structured SZ absorption at 258 to 299 nm and a weaker 369 to 413 nm system with 420 cm-i average vibrational spacings which is probably due to SJ. INTRODUCTION

The photochemistry of dichlorodisulfane, S2C12,has been the subject of several studies. McGrath reported the production of vibrationally excited Sz from the flash photolysis of SzClz along with a diffuse optical absorption band system in the region 391 to 442 nm which was assigned to the chlorodisulfanyl radical, SSCI (1). However, Donovan et al., reassigned this diffuse band system to Sp on the basis of kinetic studies (2). Herring et al., observed an ESR spectrum which was attributed to SSCl in inert gas matrices formed from the photodissociation of &Clz by a high pressure mercury arc (3). Finally, Johnson and Setser postulated the formation of SSCl radical after observing the formation of vibrationally excited HCl in the reaction of hydrogen atoms with SZC~Z (4). This study was originally undertaken as an attempt to obtain the optical absorption spectrum of the molecular anion Sz which is formed from the reaction of alkali metal atoms with &C~Z (5). Although the absorption spectrum of M+&- was not observed, two absorptions due to reaction products were found and they will be described here. EXPERIMENTAL

METHOD

The closed cycle refrigerator, vacuum system and manometric procedures have been previously described (6). Dichlorodisulfane (Aldrich, 97%), carbonyl sulfide (Matheson), carbon disulfide (Mallinckrodt, AR) and hydrogen sulfide (Matheson) were each purified prior to sample preparation by outgassing under liquid nitrogen during several freeze-thaw cycles. Argon (Air Products 99.9957) o was used without further purification. Matrix gas to reactant gas ratios (M/R) ranged from 200/l to 500/l. Samples were typically deposited at 2 to 3 mmoles/hr onto a sapphire window held at 20 K for 5 hr. Spectra were recorded throughout the experiment on a Cary 17 spectrophotometer. 1Undergraduate research student. 342 0022-2852/18/0723-0342$02.00/O Copyright

@ 1978 by Academic

All rights of reproduction

Press. Inc.

in any form reserved.

ABSORPTION

SPECTRUM

343

OF S,Cl

Atomic beams of lithium, sodium and cesium were generated as described in the previous paper (5) and codeposited with the argon/reagent sample for 4 hr. A high pressure mercury arc lamp equipped with a water bath filter and quartz windows was used to photolyze

selected samples during the deposition

period.

RESULTS

Optical precursors

absorption

experiments

which will be described

were

done with

four different

sulfur

containing

in turn.

(b)

(cl

----i__(d)

I

I

380

400

440

420 WAVELENGTH

480

(nm)

FIG. 1. Absorption spectra of new species derived from S&12 in solid argon at 20 K. (a) Li f Ar/SzClt = 500/l ; (b) Na + Ar/S$& = 200/l ; (c) Cs + Ar/SX12 = 200/l ; (d) Ar/S&h = 200/l + hv &wing deposition.

344

WIGHT AND ANDREWS

A total of 11 experiments were performed using dichlorodisulfane as the reagent. Spectra recorded after deposition of 2 mmoles of Ar/s~cl~ = 200/l sample revealed three very strong absorptions due to SXl, at 203, 258, and 299 nm. In order to resolve more completely the structure on the 203 nm band, and Ar/SXlz = 5000/l sample was examined ; eight vibronic bands were resolved from 194 to 206 nm with spacings ranging from 350 to 400 cm-‘. No absorption was observed in the 300 to 500 nm region. Two experiments were performed with lithium and Ar/S&12 = 500/l samples. In each case, a new band system was observed between 389 and 456 nm with vibronic spacings from 450 to 490 cm-‘. The absorption is illustrated in Fig. l(a) and the positions and spacings are listed in Table I. Sodium was reacted with Ar,&C12 samples in three experiments, and the same band system appeared, within experimental error, f10 cm-‘, which is shown in Fig. l(b). Three experiments were conducted with cesium as the alkali metal reagent. The first, using

Ar/S&&

with lithium

= 200/l,

the second experiment Ar,&C& absorbance

exhibited

the same new structured

absorption

and sodium, which is shown in Fig. l(c). This absorption

= 5000/l

using Ar/S&12

sample

where

= 500/l

the parent

band

and absent

in the third run with an

absorptions

were greater

than

three

units.

Two studies were done depositing

Ar/S&12

= 200/l

samples at 20 K for photolysis

with a high pressure mercury arc. Spectra recorded after a 4.5 min photolysis of deposited sample gave a hint of absorption continued

found

was weaker in

deposition

of 8 mmoles of sample luith photolysis

the same band system produced

in the metal experiments,

over a 3 hr period revealed but with less absorbance,

is shown in Fig. 1 (d).

TABLE I Absorption Band Positions and Spacings Produced from SzClz a

h bun)

;(cm-1

456.1

21 925

446.4

22 416

436.8

22 894

478

427.1

23 381

487

419.6

23 832

451

411.4

24 307

475

403.7

24 771

464

336.5

25 221

450

389.1

25 700

479

%bso1ute

of 6 mmole

peaks in the 389 to 4.56 nm region; however,

)

spacings

accuracy +_ 20 cm-'.

491

-1

(cm

)

as

ABSORPTION

FIG. 2. Absorption during

deposition

spectra at 20 K.

of sulfur

SPECTRUM

species

produced

by

345

OF S,Cl

photolysis

of Ar/OCS

= 400/l

sample

OCS Four experiments were done with carbonyl sulfide. After deposition of an Ar/OCS = 400/l sample for 1 hr, a weak band system due to OCS was observed at 198 nm with weak 400 cm-’ spaced vibronic structure. In three of these experiments, sodium was codeposited with the OCS reagent during photolysis. In the fourth, an Ar/OCS = 400/l sample was deposited with concurrent photolysis and no sodium. In all four studies, two band systems were observed and the presence of sodium made no difference in the spectra. The first band exhibited two weak superimposed vibronic progressions between TABLE Absorption

Band

Positions

and Spacings

1 (nm)

G (cm-’ 1

410.3

24

II Produced

by Photolysis

spacings

372

403.9

24

759

386

397.3

25

170

411

390.5

25

608

438

384.4

26

015

407

413.1

24

207

406.2

24

618

411

400.5

24

969

351

394.8

25

329

360

388.2

25

760

431

381.8

26

192

432

375.2

26

649

457

368.9

27

108

459

-1 (cm )

of OCS

346

WIGHT AND ANDREWS

369 and 413 nm with average spacings of about 430 cm-‘. This system is shown in Fig. 2 and the band positions are listed in Table II. The second system contained a series of vibronic bands from 258 to 299 nm with spacings ranging from 330 to 370 cm-‘, which is also shown in Fig. 2. The latter system is in excellent agreement with the progression assigned to Sz in matrices (7).

One experiment was performed depositing carbon disulfide and argon onto the cold window. Spectra taken before photolysis showed a parent absorption system at 295 to 325 with six vibronic bands spaced 540 cm-* apart and split into two or more components. The sample was photolyzed in situ for 0.5 hr followed by 1.5 hr of photolysis during deposition. No new absorption bands were observed after either photolysis. The matrix was then annealed to 45 K and final spectra recorded. The site split vibronic bands on the CSZ absorption joined to form one set of broader vibronic bands with 540 cm-’ spacings.

Three experiments were performed by depositing H2S and argon onto the cold window. No parent bands were observed and no product absorptions were observed after 3 hr of photolysis during deposition. In one of the experiments, an atomic beam of sodium was deposited during reagent deposition and photolysis, but no new absorptions were observed. DISCUSSION

The band systems derived from the SZC~Zand OCS precursors

will be described here.

389 to 456 nm System The band system obtained from S&& was produced both by alkali metal matrix reactions and by photolysis. This chemical evidence suggests SZCl as the absorbing species, produced by reactions (1) and (2), respectively. SzClz + M --$ MC1 + S&l,

(1)

SC12 + hv(220-1000

(2)

nm) + Cl + S2Cl.

A large number of chloride abstraction reactions have been performed in this laboratory using alkali metal atom matrix reactions (8), and reaction (1) is expected to be a favorable reaction. The absence of a metal shift in the spectra suggests, but does not prove, the absence of alkali metal in the product species. However, the observation of the band system in photolysis experiments without alkali metal does confirm the absence of metal in the new species. Recent matrix photolysis studies of chlorosulfanes demonstrated that mercury arc photolysis selectively breaks S-Cl bonds (9), in contrast to the proposed fission of the weak S-S bond in the gas phase (Z), and the &Cl radical has been observed by ESR in one of the matrix studies (3). The matrix photolysis data support the formation of &Cl in these experiments.

ABSORPTION

SPECTRUM

OF S&l

347

On the basis of the alkali metal matrix reactions and the matrix photolysis of S&12, the 389 to 456 nm absorption is assigned to the chlorodisulfanyl radical S&l. The vibronic progression for S&l has 450 to 490 cm-’ vibrational spacings giving U’ 2 490 cm-’ which probably involves the S-Cl stretching mode of the excited S&l species. It is concluded that the original assignment of a diffuse 391 to 442 nm gas-phase band system to the SC.1 free radical (1) is correct, since reactions (1) and (2) cannot produce the Sa species suggested by later workers (2). Although the laser-induced photoluminescence spectrum of M+$ has been observed from alkali metal-SzClz matrix samples (5), this species requires three matrix reactions for its production, and the concentration of MfS- in these samples must be considerably less than &Cl. Therefore, the absorption spectrum of Sz from 380 to 460 nm with 350 f 30 cm-’ vibrational spacings (10) is expected to be much weaker than the &Cl absorption, and the former weak absorption would be masked by the latter strong absorption. 368 to 413 nm System When carbonyl sulfide and argon were deposited onto the cold window during photolysis with a high pressure mercury arc, Sz absorption bands were observed, indicating cleavage of the C-S bond to form sulfur atoms which then recombine with other sulfur atoms during condensation. Another weaker absorption was observed in the region 368 to 413 nm which exhibited two overlapping vibronic progressions with approximately 420 cm-r spacings. Since carbon monoxide does not display any absorption in this region, the band is probably due to a higher aggregate of sulfur atoms. Meyer et al., assigned a gas phase absorption with 420 cm-’ spacings in the region 350 to 450 nm to Ss, and produced a similar absorption with vibronic structure from the photolysis of SX12 in a krypton matrix at 20 K (9). The position and spacings of the present vibronic progression suggest that it is due to SI; the vibrational spacing, 420 cm-‘, is reasonable for the excited state symmetric stretching mode v’r for SI, in view of the ground state Y”~mode for Ss at 585 cm-r (II). Experiments were performed with the sulfur atom sources, H2.S and CS2, in an attempt to reproduce the results obtained with OCS, but no 368 to 413 nm absorption was observed. In the sodium experiments with OCS and mercury arc photolysis, which produced SZ and the 368 to 413 nm absorption attributed to Sa, the Na+&- and Na+Ss- species were probably also produced. However, the Na+St- absorption coincides with the Sa absorption, and any Na+S.i absorption is probably masked by the stronger SI progression. Finally, it has been shown that Sa- is a photosensitive species, and the failure to observe Na+&- at 620 nm (10) in the sodium experiments with OCS and photolysis is probably due to its photodecomposition. CONCLUSIONS

Optical absorption studies of the alkali metal atom-dichlorodisulfane matrix reaction revealed a 389 to 456 nm progression with 470 to 490 cm-’ spacings. Observation of the same band system after deposition of an Ar,&J& sample with concurrent mercury arc photolysis indicates that this absorption is due to the chlorodisulfanyl radical, S&l. Photolysis of Ar/OCS samples during deposition produced the well-known 258 to 299

348

WIGHT

AND

ANDREWS

nm SZ absorption and a 368 to 413 nm band spacings which is tentatively assigned to SI.

system

with approximately

420 cm-’

ACKNOWLEDGMENT The authors RECEIVED :

gratefully

December

acknowledge

support

from the National

Science Foundation.

28, 1977 REFERENCES

W. D. MCGRATH, J. Chem. Phys. 33, 297-298 (1960). R. J. DONOVAN, D. HTJSAINAND P. T. JACKSON, Trans. Faraday SOL. 64, 1798-1805 (1968). F. G. HERRING, C. A. MCDOWELL, AND J. C. TAIT, J. Chem. Phys. 57, 45644570 (1972). R. L. JOHNSONAND D. W. SETSER, Chew. Phys. Lett. 3, 207-211 (1969). C. A. WIGHT, H. WILLNER, AND L. ANDREWS, J. Mol. Spectrosc., previous paper. L. ANDREWS, J. Chem. Phys. 63, 44654469 (1975). L. BREWER, G. D. BABSON, AND B. MEYER, J. Chem. Phys. 42, 1385-1389 (1965). L. ANDREWS AND D. W. SMITH, J. Chem. Phys. 53, 29562966 (1970) and references therein. B. MEYER, T. STROYER-HANSEN,AND T. V. OOMEN, J. Mol. Spectrosc. 42, 335-343 (1972). C. A. SAWICKI AND D. B. FITCHEN, J. Chem. Phys. 65, 44974507 (1976). 11. A. G. HOPKINS, S. TANG, AND C. W. BROWN, J. Amer. Chem. Sot. 95, 3486-3490 (1973) and published results.

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

un-