- Email: [email protected]
CO⋯H2O bonding in and on porous ices
Vibrational Spectroscopy 16 Ž1998. 85–88
Short communication
CO PPP H 2 O bonding in and on porous ices A. Givan a , A. Loewenschuss a
a,)
, C.J. Nielsen
b
Department of Inorganic and Analytical Chemistry, The Hebrew UniÕersity of Jerusalem, Jerusalem 91904, Israel b Department of Chemistry, UniÕersity of Oslo, Blindern, N-0315 Oslo, Norway Received 24 July 1997; accepted 20 October 1997
Abstract Spectra of H 2 O in solid CO are presented and compared to results obtained for CO adsorbed on different water ices. By the shape of the n ŽOH. features, CO association to well separated dangling OH bonds and to water polymeric structures may be distinguished. It is suggested that the CO clusters, formed by CO deposition onto ices of bulk porosity, surround narrow, hair like protrusions of the ice voids. q 1998 Elsevier Science B.V. Keywords: Infrared spectrometry; Water ices; CO)H 2 O complexes; CO adsorption
The infrared absorption of the CO stretching mode was recently shown to be a sensitive indicator of the morphology and porosity of pure and mixed ices w1–3x. The attachment of CO molecules to H 2 O in these ices results from diffusion induced by warming to T ) 30 K of a CO layer deposited onto them. For this complexation two cases may be distinguished: ŽA. An ice prepared by depositing a 4:1 Ar:H 2 O mixture at 5 K demonstrated, in addition to the main coupled ‘3 m’ band, infrared features at 3704 and 3720 cmy1 corresponding to uncoupled or ‘dangling’ O–H bonds of 2-coordinated water molecules Žone hydrogen bond Õia O and one Õia H. and 3-coordinated water molecules Žtwo hydrogen bonds Õia O and one Õia H. w4x. When such an ice was
) Corresponding author. Tel.: q972-2-6585313; fax: q972-26585319; e-mail: [email protected].
covered with a solid CO layer and subsequently warmed to above 30 K, two new relatively sharp infrared bands appeared at 3692 and 3629 cmy1 and were assigned to CO)H 2 O species. A similar doublet, attributed to the OC)H–OH complex, was observed in rare gas matrices w5–13x, e.g. at 3723 and 3627 cmy1 in argon w5x. The COrice features at 3692 and 3629 cmy1 were interpreted in terms of bonding of CO to the free, dangling OH bonds on the microporous surfaces of the deposited ice w1x Žsurface porosity’’.. The fact that the doublet splitting retains a magnitude similar to the n 3rn 1 frequency difference in the H 2 O monomer, is an indication of CO bonding to distinct, well separated OH bonds. Temperature induced intensity changes of these bands followed that of the analogous n ŽCO. band at 2153 cmy1 . The latter is blue shifted from the n ŽCO. peak at 2138.5 cmy1 and the CO)H 2 O dimer band at 2149 cmy1 observed in argon matrices
0924-2031r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 4 - 2 0 3 1 Ž 9 7 . 0 0 0 4 4 - 1
86
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
part at 2148 cmy1 . This behavior was ascribed w2,5x to CO clusters distributed in the ice bulk pores, without specifying the exact nature of the CO PPP H 2 O bonding. Similarly, ices produced from premixed COrH 2 O also showed only a single band attributable to CO)H 2 O species in the OH stretching region at 3623 cmy1 . The temperature dependence is also similar: Upon warming, it red shifted to 3618 cmy1 along with its n ŽCO. counterpart at 2150 cmy1 w2,13,14x. In the following we discuss our results of experiments involving the trapping of H 2 O species in solid CO and relate them to the two cases presented above. The present results are summarized in Table 1 together with relevant previous assignments. Experimental details follow those given elsewhere w2x. In short, spectra of gaseous H 2 OrCO mixtures, de-
Fig. 1. The infrared spectrum of the free OH’’ region of ices produced by deposition of a 4:1 NerH 2 O mixture. ŽA. As deposited at 5 K. ŽB. After warming to 30 K to release the Ne, then recooling to 5 K, followed by covering the sample with a CO deposition, and subsequently warming to 30 K to release the external non-bonded CO. Spectrum recorded after recooling to 5 K. ŽC. After additional warming of sample B to 40 K and recooling to 5 K.
w5x and thus both spectral regions indicate the possibility of CO bonding to two OH bonds. ŽB. An ice produced by release of neon from a mixed NerH 2 O deposited layer, was shown to possess properties of bulk porosity w2x. As produced, it demonstrated only remnants of the uncoupled OH bands at 3720 and 3704 cmy1 ŽFig. 1A.. Upon CO deposition onto this ice at 5 K, followed by warming to 30 K, a single new broad band, ascribed to CO)H 2 O species, appeared at 3670 cmy1 ŽFig. 1B.. Further warming to 40 K ŽFig. 1C. red shifted this absorption to 3640 cmy1 . At 50 K this band completely disappeared together with its n ŽCO. counter-
Fig. 2. The infrared spectrum of the n ŽOH. stretching region of a sample produced by deposition of a 10:1 COrH 2 O mixture at 5 K. ŽA. As deposited at 5 K. ŽB. Warmed to 26 K and recooled to 5 K. ŽC. Warmed to 33 K and recooled to 5 K.
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
87
Table 1 Summary of band assignments Band Žcmy1 .
Assignment
Ref.
3720 3704 3692, 3629 3723, 3627 3670 Ž3640. 3623 Ž3618. 3692.7, 3674.2, 3609 3643, 3400 3250 2153 2150 2149 2138.5 1638 1610.5
‘dangling’ OH of 2-coordinated water molecules on ice surface ‘dangling’ OH of 3-coordinated water molecules on ice surface n ŽOH. of CO)H 2 O species on ice surface n ŽOH. of CO)H 2 O species in argon matrix n ŽOH. of CO)H 2 O species on bulk porous ice ŽT shift. n ŽOH. of CO)H 2 O in COrH 2 O mixed ice ŽT shift. n ŽOH. of H 2 O molecular species Ždimers. in CO matrix n ŽOH. of H 2 O polymers in CO matrix n ŽOH. of amorphous ice n ŽCO. of CO)H 2 O on ice surface ŽCO attached to two OH bonds. n ŽCO. of CO)H 2 O in COrH 2 O mixed ice ŽT shift. n ŽCO. of CO)H 2 O dimer in argon matrix n ŽCO. in argon matrix n 2 of H 2 O in water polymeric species in CO matrix n 2 of H 2 O in molecular species Ždimers. in CO matrix
w4x w4x w2,3x w5x w2x this work this work this work w15x w2,3x this work w5x w5x this work this work
posited at 5 K and slowly Ž1 Krmin. warmed up to 34 K Žthe CO sublimation temperature., were recorded on a Bruker IFS-88 interferometer, coadding 128 scans, with resolutions of 0.5 to 2 cmy1 . The OH stretching region of a typical sample Žseveral percent H 2 O in the CO matrix, Fig. 2A. reveals spectral features which may roughly be divided into two groups: The sharper and higher peak bands in the 3700–3600 cmy1 region Žtwo narrow lines at 3692.7 and 3609 cmy1 and two broader ones at 3674.2 and a shoulder at 3658 cmy1 . and the much broader features in the 3550–3300 cmy1 region, centered around 3360 cmy1 and with a peak at 3500 cmy1 . Upon annealing the sample to 26 K ŽFig. 2B. the resolved structure of the first group disappeared leaving a 35 cmy1 wide feature at 3652 cmy1 and a 200 cmy1 wide band centered around 3400 cmy1 . While this general picture did not essentially change upon warming to 33 K ŽFig. 2C., the narrower band red shifted to 3643 cmy1 , and a new feature around 3250 cmy1 gradually emerged. The much weaker n 2 bending region presents a similar transition from narrow well resolved absorptions at 1610.5 and 1632 cmy1 at 5 K ŽFig. 3A., to a single very broad feature centered at 1638 cmy1 ŽFig. 3B.. The sharp features at 3692.7, 3674.2, 3609 and 1610.5 cmy1 are attributed to distinct H 2 O species Žmostly dimers. w12x in a CO matrix, while the broader features at 3643, 3400 and 1638 cmy1 are attributed to higher H 2 O
Fig. 3. The n 2 ŽH 2 O. bending mode region of a sample produced by the deposition of a 10:1 COrH 2 O mixture at 5 K. ŽA. As deposited. ŽB. Warmed to 26 K and recooled to 5 K.
88
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
polymers. The 3250 cmy1 absorption is typical of ŽH 2 O.as w15x. Our new results presented here for H 2 O in solid CO clarify the attachment of CO within ices of bulk porosity containing CO clusters distributed within its pores Žcase ŽB., above.. The 3640 cmy1 infrared band resembles in shape and position the 3643 cmy1 absorption of polymeric H 2 O species trapped in solid CO. In comparison with case ŽA. and ŽB., it is clear that of the two distinguishable types of CO PPP H 2 O bonding, the CO clusters inside the bulk pores are not bonded to separated OH bonds, but rather to ice structures resembling H 2 O polymers. It is therefore suggested that the CO clusters surround narrow, hair like protrusions of the ice voids, as suggested by Laufer et al. w16x, producing an infrared spectrum similar to that of H 2 O polymers trapped in CO.
Acknowledgements A. L. acknowledges a Visiting Scientist scholarship from the Norwegian Research Council.
References w1x J.P. Devlin, J. Phys. Chem. 96 Ž1992. 6185. w2x A. Givan, A. Loewenschuss, C.J. Nielsen, Vib. Spectrosc. 12 Ž1996. 1. w3x A. Givan, A. Loewenschuss, C.J. Nielsen, Chem. Phys. Lett. 275 Ž1997. 98. w4x V. Buch, J.P. Devlin, J. Chem. Phys. 94 Ž1991. 4091. w5x A. Givan, A. Loewenschuss, C.J. Nielsen, J. Chem. Soc. Faraday Trans. 92 Ž1996. 4927. w6x L. Andrews, R.T. Arlinghaus, G.L. Johnson, J. Chem. Phys. 78 Ž1978. 6347. w7x M. Diem, E.K.C. Lee, J. Phys. Chem. 86 Ž1982. 4507. w8x B. Nelander, J. Phys. Chem. 89 Ž1985. 827. w9x T.L. Tso, E.K.C. Lee, J. Phys. Chem. 89 Ž1985. 1612. w10x T.L. Tso, E.K.C. Lee, J. Phys. Chem. 89 Ž1985. 1618. w11x H. Dubost, L. Abouaf-Marguin, Chem. Phys. Lett. 17 Ž1972. 269. w12x W. Hagen, A.G.G.M. Tielens, J. Chem. Phys. 75 Ž1981. 4198. w13x M.E. Palumbo, G. Strazzulla, Astron. Astrophys. 269 Ž1994. 568. w14x S.A. Sanford, L.J. Allamandolla, A.G.G.M. Tielens, G.J. Valero, Astrophys. J. 329 Ž1988. 498. w15x A. Givan, A. Loewenschuss, C.J. Nielsen, J. Phys. Chem., in press. w16x D. Laufer, E. Kochavi, A. Bar-Nun, Phys. Rev. B 36 Ž1987. 9219.
Short communication
CO PPP H 2 O bonding in and on porous ices A. Givan a , A. Loewenschuss a
a,)
, C.J. Nielsen
b
Department of Inorganic and Analytical Chemistry, The Hebrew UniÕersity of Jerusalem, Jerusalem 91904, Israel b Department of Chemistry, UniÕersity of Oslo, Blindern, N-0315 Oslo, Norway Received 24 July 1997; accepted 20 October 1997
Abstract Spectra of H 2 O in solid CO are presented and compared to results obtained for CO adsorbed on different water ices. By the shape of the n ŽOH. features, CO association to well separated dangling OH bonds and to water polymeric structures may be distinguished. It is suggested that the CO clusters, formed by CO deposition onto ices of bulk porosity, surround narrow, hair like protrusions of the ice voids. q 1998 Elsevier Science B.V. Keywords: Infrared spectrometry; Water ices; CO)H 2 O complexes; CO adsorption
The infrared absorption of the CO stretching mode was recently shown to be a sensitive indicator of the morphology and porosity of pure and mixed ices w1–3x. The attachment of CO molecules to H 2 O in these ices results from diffusion induced by warming to T ) 30 K of a CO layer deposited onto them. For this complexation two cases may be distinguished: ŽA. An ice prepared by depositing a 4:1 Ar:H 2 O mixture at 5 K demonstrated, in addition to the main coupled ‘3 m’ band, infrared features at 3704 and 3720 cmy1 corresponding to uncoupled or ‘dangling’ O–H bonds of 2-coordinated water molecules Žone hydrogen bond Õia O and one Õia H. and 3-coordinated water molecules Žtwo hydrogen bonds Õia O and one Õia H. w4x. When such an ice was
) Corresponding author. Tel.: q972-2-6585313; fax: q972-26585319; e-mail: [email protected].
covered with a solid CO layer and subsequently warmed to above 30 K, two new relatively sharp infrared bands appeared at 3692 and 3629 cmy1 and were assigned to CO)H 2 O species. A similar doublet, attributed to the OC)H–OH complex, was observed in rare gas matrices w5–13x, e.g. at 3723 and 3627 cmy1 in argon w5x. The COrice features at 3692 and 3629 cmy1 were interpreted in terms of bonding of CO to the free, dangling OH bonds on the microporous surfaces of the deposited ice w1x Žsurface porosity’’.. The fact that the doublet splitting retains a magnitude similar to the n 3rn 1 frequency difference in the H 2 O monomer, is an indication of CO bonding to distinct, well separated OH bonds. Temperature induced intensity changes of these bands followed that of the analogous n ŽCO. band at 2153 cmy1 . The latter is blue shifted from the n ŽCO. peak at 2138.5 cmy1 and the CO)H 2 O dimer band at 2149 cmy1 observed in argon matrices
0924-2031r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 4 - 2 0 3 1 Ž 9 7 . 0 0 0 4 4 - 1
86
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
part at 2148 cmy1 . This behavior was ascribed w2,5x to CO clusters distributed in the ice bulk pores, without specifying the exact nature of the CO PPP H 2 O bonding. Similarly, ices produced from premixed COrH 2 O also showed only a single band attributable to CO)H 2 O species in the OH stretching region at 3623 cmy1 . The temperature dependence is also similar: Upon warming, it red shifted to 3618 cmy1 along with its n ŽCO. counterpart at 2150 cmy1 w2,13,14x. In the following we discuss our results of experiments involving the trapping of H 2 O species in solid CO and relate them to the two cases presented above. The present results are summarized in Table 1 together with relevant previous assignments. Experimental details follow those given elsewhere w2x. In short, spectra of gaseous H 2 OrCO mixtures, de-
Fig. 1. The infrared spectrum of the free OH’’ region of ices produced by deposition of a 4:1 NerH 2 O mixture. ŽA. As deposited at 5 K. ŽB. After warming to 30 K to release the Ne, then recooling to 5 K, followed by covering the sample with a CO deposition, and subsequently warming to 30 K to release the external non-bonded CO. Spectrum recorded after recooling to 5 K. ŽC. After additional warming of sample B to 40 K and recooling to 5 K.
w5x and thus both spectral regions indicate the possibility of CO bonding to two OH bonds. ŽB. An ice produced by release of neon from a mixed NerH 2 O deposited layer, was shown to possess properties of bulk porosity w2x. As produced, it demonstrated only remnants of the uncoupled OH bands at 3720 and 3704 cmy1 ŽFig. 1A.. Upon CO deposition onto this ice at 5 K, followed by warming to 30 K, a single new broad band, ascribed to CO)H 2 O species, appeared at 3670 cmy1 ŽFig. 1B.. Further warming to 40 K ŽFig. 1C. red shifted this absorption to 3640 cmy1 . At 50 K this band completely disappeared together with its n ŽCO. counter-
Fig. 2. The infrared spectrum of the n ŽOH. stretching region of a sample produced by deposition of a 10:1 COrH 2 O mixture at 5 K. ŽA. As deposited at 5 K. ŽB. Warmed to 26 K and recooled to 5 K. ŽC. Warmed to 33 K and recooled to 5 K.
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
87
Table 1 Summary of band assignments Band Žcmy1 .
Assignment
Ref.
3720 3704 3692, 3629 3723, 3627 3670 Ž3640. 3623 Ž3618. 3692.7, 3674.2, 3609 3643, 3400 3250 2153 2150 2149 2138.5 1638 1610.5
‘dangling’ OH of 2-coordinated water molecules on ice surface ‘dangling’ OH of 3-coordinated water molecules on ice surface n ŽOH. of CO)H 2 O species on ice surface n ŽOH. of CO)H 2 O species in argon matrix n ŽOH. of CO)H 2 O species on bulk porous ice ŽT shift. n ŽOH. of CO)H 2 O in COrH 2 O mixed ice ŽT shift. n ŽOH. of H 2 O molecular species Ždimers. in CO matrix n ŽOH. of H 2 O polymers in CO matrix n ŽOH. of amorphous ice n ŽCO. of CO)H 2 O on ice surface ŽCO attached to two OH bonds. n ŽCO. of CO)H 2 O in COrH 2 O mixed ice ŽT shift. n ŽCO. of CO)H 2 O dimer in argon matrix n ŽCO. in argon matrix n 2 of H 2 O in water polymeric species in CO matrix n 2 of H 2 O in molecular species Ždimers. in CO matrix
w4x w4x w2,3x w5x w2x this work this work this work w15x w2,3x this work w5x w5x this work this work
posited at 5 K and slowly Ž1 Krmin. warmed up to 34 K Žthe CO sublimation temperature., were recorded on a Bruker IFS-88 interferometer, coadding 128 scans, with resolutions of 0.5 to 2 cmy1 . The OH stretching region of a typical sample Žseveral percent H 2 O in the CO matrix, Fig. 2A. reveals spectral features which may roughly be divided into two groups: The sharper and higher peak bands in the 3700–3600 cmy1 region Žtwo narrow lines at 3692.7 and 3609 cmy1 and two broader ones at 3674.2 and a shoulder at 3658 cmy1 . and the much broader features in the 3550–3300 cmy1 region, centered around 3360 cmy1 and with a peak at 3500 cmy1 . Upon annealing the sample to 26 K ŽFig. 2B. the resolved structure of the first group disappeared leaving a 35 cmy1 wide feature at 3652 cmy1 and a 200 cmy1 wide band centered around 3400 cmy1 . While this general picture did not essentially change upon warming to 33 K ŽFig. 2C., the narrower band red shifted to 3643 cmy1 , and a new feature around 3250 cmy1 gradually emerged. The much weaker n 2 bending region presents a similar transition from narrow well resolved absorptions at 1610.5 and 1632 cmy1 at 5 K ŽFig. 3A., to a single very broad feature centered at 1638 cmy1 ŽFig. 3B.. The sharp features at 3692.7, 3674.2, 3609 and 1610.5 cmy1 are attributed to distinct H 2 O species Žmostly dimers. w12x in a CO matrix, while the broader features at 3643, 3400 and 1638 cmy1 are attributed to higher H 2 O
Fig. 3. The n 2 ŽH 2 O. bending mode region of a sample produced by the deposition of a 10:1 COrH 2 O mixture at 5 K. ŽA. As deposited. ŽB. Warmed to 26 K and recooled to 5 K.
88
A. GiÕan et al.r Vibrational Spectroscopy 16 (1998) 85–88
polymers. The 3250 cmy1 absorption is typical of ŽH 2 O.as w15x. Our new results presented here for H 2 O in solid CO clarify the attachment of CO within ices of bulk porosity containing CO clusters distributed within its pores Žcase ŽB., above.. The 3640 cmy1 infrared band resembles in shape and position the 3643 cmy1 absorption of polymeric H 2 O species trapped in solid CO. In comparison with case ŽA. and ŽB., it is clear that of the two distinguishable types of CO PPP H 2 O bonding, the CO clusters inside the bulk pores are not bonded to separated OH bonds, but rather to ice structures resembling H 2 O polymers. It is therefore suggested that the CO clusters surround narrow, hair like protrusions of the ice voids, as suggested by Laufer et al. w16x, producing an infrared spectrum similar to that of H 2 O polymers trapped in CO.
Acknowledgements A. L. acknowledges a Visiting Scientist scholarship from the Norwegian Research Council.
References w1x J.P. Devlin, J. Phys. Chem. 96 Ž1992. 6185. w2x A. Givan, A. Loewenschuss, C.J. Nielsen, Vib. Spectrosc. 12 Ž1996. 1. w3x A. Givan, A. Loewenschuss, C.J. Nielsen, Chem. Phys. Lett. 275 Ž1997. 98. w4x V. Buch, J.P. Devlin, J. Chem. Phys. 94 Ž1991. 4091. w5x A. Givan, A. Loewenschuss, C.J. Nielsen, J. Chem. Soc. Faraday Trans. 92 Ž1996. 4927. w6x L. Andrews, R.T. Arlinghaus, G.L. Johnson, J. Chem. Phys. 78 Ž1978. 6347. w7x M. Diem, E.K.C. Lee, J. Phys. Chem. 86 Ž1982. 4507. w8x B. Nelander, J. Phys. Chem. 89 Ž1985. 827. w9x T.L. Tso, E.K.C. Lee, J. Phys. Chem. 89 Ž1985. 1612. w10x T.L. Tso, E.K.C. Lee, J. Phys. Chem. 89 Ž1985. 1618. w11x H. Dubost, L. Abouaf-Marguin, Chem. Phys. Lett. 17 Ž1972. 269. w12x W. Hagen, A.G.G.M. Tielens, J. Chem. Phys. 75 Ž1981. 4198. w13x M.E. Palumbo, G. Strazzulla, Astron. Astrophys. 269 Ž1994. 568. w14x S.A. Sanford, L.J. Allamandolla, A.G.G.M. Tielens, G.J. Valero, Astrophys. J. 329 Ž1988. 498. w15x A. Givan, A. Loewenschuss, C.J. Nielsen, J. Phys. Chem., in press. w16x D. Laufer, E. Kochavi, A. Bar-Nun, Phys. Rev. B 36 Ž1987. 9219.