ARTICLE pubs.acs.org/JPCA
Infrared Spectrum of the CH3OCH2 Radical in Solid Argon Yu Gong and Lester Andrews* Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904-4319, United States ABSTRACT: The methoxymethyl radical, CH3OCH2, is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH3OCH3 in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm1, which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The OCH2 bond length is calculated to be 0.07 Å shorter than the CH3O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH3OCH2 radical with the formation of HCO radical and CH4, which is different from the decomposition mechanism of CH3OCH2 radical to H2CO and CH3 radical proposed for the gas phase process.
’ INTRODUCTION The importance of dimethyl ether (DME) in combustion and atmospheric chemistry has been well recognized in recent years due to its potential value as diesel fuel and fuel additives.1 During the oxidation of DME, methoxymethyl radical, CH3OCH2, which is produced via the reaction of DME and OH radical, is believed to be an important precursor intermediate for the formation of formaldehyde and other hydrocarbons involved in the combustion process.2 Hence investigations on the structure and reactions of the CH3OCH2 radical are important in understanding the oxidation process of DME. A series of kinetic studies as well as theoretical interpretations regarding the reaction of methoxymethyl radical and O2 as well as other molecules involved in the atmospheric and combustion process have been carried out, which have provided detailed insight into the mechanism of ether oxidation in the atmosphere.310 However, spectroscopic studies on the structure of this radical are quite limited. UV spectra of the CH3OCH2 radical have been reported in the gas phase, which exhibited broad bands centered around 200 and 300 nm.6,11 Ab initio calculations at the multireference configuration interaction level of theory indicated that the former absorption should be attributed to the transition from the doubly occupied lone pair orbitals of oxygen to the singly occupied p orbital of carbon while transitions from the singly occupied orbital to the virtual and diffuse orbitals account for the latter band.12 No other studies have been performed on this radical except for some theoretical calculations mostly involving reaction mechanisms.710,1316 The matrix isolation technique has proved to be a powerful tool for trapping transient species such as radicals, and structural information can be obtained especially when it is combined with infrared spectroscopy.17 Sander et al. performed an experimental and theoretical study on the reactions of DME and atomic oxygen in an argon matrix, and two conformers of methoxymethanol (CH3OCH2OH) were identified. However, no absorption could be assigned to the CH3OCH2 radical.18 In this paper, we present a combined matrix isolation infrared spectroscopic and theoretical study of the CH3OCH2 radical, which is produced during the codeposition of DME with laser-ablated metal plume vacuum-UV radiation. The identification of this radical is supported r 2011 American Chemical Society
by experiments with CD3OCD3 sample as well as theoretical vibrational frequency and intensity calculations.
’ EXPERIMENTAL AND THEORETICAL METHODS The new radical species is produced during the codeposition of DME with laser-ablated metal plume radiation in excess argon at 4 K, and these experiments have been described previously.19 In this case, the important experimental event is the production of vacuumUV radiation in the plume of light generated by the pulsed laser (1064 nm, 10 Hz repetition rate with 10 ns pulse width) focused onto the metal target. The metals reported here gave the highest yield of metal-independent product absorptions. Previous work has documented the presence of high-energy radiation in the laser ablation plume in these matrix isolation experiments for the formation of radicals and cations from the precursor.20 Laser-ablated metal atoms were necessarily codeposited with the samples (34 mmol of argon, (Matheson, research) containing 0.5% CH3OCH3 (Aldrich) or CD3OCD3 (MSD ISOTOPES)) onto the CsI cryogenic window. However, metal-dependent chemical reaction product absorptions are not the subject of the present investigation. FTIR spectra were recorded at 0.5 cm1 resolution on a Nicolet 750 FTIR instrument with 0.5 cm1 accuracy using a HgCdTe range B detector. Matrix samples were annealed at different temperatures, and selected samples were subjected to broad band photolysis with different filters by a medium-pressure mercury arc street lamp (Philips, 175 W) with the outer globe removed. Density functional calculations were performed with the Gaussian 09 program.21 The B3LYP22 and BPW9123 density functionals and the 6-311þþG(d, p) and 6-311þþG(3df, 3pd) basis sets24 were used for all of the atoms. The geometrical parameters of the new product molecule were fully optimized, and the harmonic vibrational frequencies were obtained analytically at the optimized structures. Anharmonic calculations were also done at the B3LYP level of theory using a second-order vibrational perturbation approach as implemented by the Gaussian 09 software package.21 Received: February 25, 2011 Published: March 22, 2011 3029
dx.doi.org/10.1021/jp2018692 | J. Phys. Chem. A 2011, 115, 3029–3033
The Journal of Physical Chemistry A
Figure 1. Infrared spectra from codeposition of CH3OCH3 in excess argon at 4 K with laser-excited metal plume radiation. All the spectra were taken right after sample deposition: (a) Tb target, 0.5% CH3OCH3; (b) Ho target, 0.5% CH3OCH3; (c) Th target, 0.5% CH3OCH3; (d) U target, 0.5% CH3OCH3. P denotes an absorption of DME.
Figure 2. Infrared spectra from codeposition of CH3OCH3 in excess argon at 4 K with laser-excited uranium metal plume radiation. (a) U radiation þ 0.5% CH3OCH3 deposition for 60 min; (b) after annealing to 30 K; (c) after λ >290 nm irradiation; (d) after λ >220 nm irradiation. P denotes absorptions of DME.
’ DISCUSSION Infrared spectra from the 4 K codeposition of DME/argon mixtures with four different laser-excited metal target irradiations are shown in Figure 1. In addition to strong bands of the DME precursor18 as well as weak metal dependent chemical reaction product absorptions, four new absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm1 were found to be independent of the metal target in all of the experiments. Subsequent work with Ti, Zr, and Hf produced the same absorptions. Figure 2 shows infrared spectra from the codeposition of laser-ablated uranium atoms with 0.5% DME in argon, which gave the highest product yield. The product spectrum after sample deposition (Figure 2, trace a) is dominated by the absorptions of HCO,25 formaldehyde, and methane as well as the four new absorptions. All of these bands decreased when the sample was annealed (Figure 2, trace b). Irradiation with λ > 290 nm mercury arc light had no effect on the bands except for a slight increase in the methane absorption. Further broad band irradiation (λ > 220 nm) substantially decreased the four new absorptions
ARTICLE
Figure 3. Infrared spectra from codeposition of CD3OCD3 in excess argon at 4 K with laser-excited uranium metal plume radiation. (a) U radiation þ 0.5% CD3OCD3 deposition for 60 min; (b) after annealing to 30 K; (c) after λ >290 nm irradiation; (d) after λ >220 nm irradiation. The asterisk denotes absorption of a metal dependent U atom and CD3OCD3 chemical reaction product.
while the HCO and methane absorptions increased. It should be noted that the UH (1423.6 cm1) and UH2 (1370.7 cm1) absorptions increased during sample annealing, which attests to the presence of H atoms in the matrix.26 To help with product identification, experiments were done with CD3OCD3 sample. Three absorptions at 1267.7, 1123.0, and 1033.3 cm1 were found to be metal independent (Figure 3) in addition to the absorptions of CD3OCD3 precorsor,18 DCO,24 CD4 and CD2O. The three new absorptions decreased upon sample annealing, and they were almost destroyed with broad band (λ > 220 nm) irradiation. An experiment with mixed CH3OCH3 and CD3OCD3 (1:1) precursor was also done, and the same 1468.1, 1253.9, 1267.7, 1226.6, 1123.0, 1033.3, and 944.4 cm1 absorptions were observed as in the pure isotopic sample experiments including CH4 and CD4. The 1468.1, 1253.9, 1226.6, and 944.4 cm1 absorptions have identical relative intensities throughout the experiments with CH3OCH3 samples, suggesting that they are different vibrational modes of the same new product. Only one CH3OCH3 molecule is involved in the formation of this new product since no additional band was observed in the mixed H/D isotopic experiment. As shown in Figure 2, trace d, both HCO and CH4 absorptions increased on broad band irradiation at the expense of the 1468.1, 1253.9, 1226.6, and 944.4 cm1 absorptions, suggesting that HCO and CH4 come from the decomposition of the new molecule observed here. Hence C2H5O must be considered for the stoichiometry of the new molecule, which absorbs at 1468.1, 1253.9, 1226.6, and 944.4 cm1. The strongest two bands at 1253.9 and 944.4 cm1 are about 80 and 20 cm1 blue-shifted from the antisymmetric and symmetric OCO stretching modes of CH3OCH3, respectively,18 and their relative infrared intensities are also comparable with those of CH3OCH3. It is reasonable to assign these two bands to the antisymmetric and symmetric OCO stretching vibrational modes of a new molecule with similar COC structural characteristics. The weak 1468.1 cm1 absorption lies in the region of CH3 deformation modes, and this band suggests the presence of a methyl group in the new molecule. Assignment of the broad band at 1226.6 cm1 is probably analogous with that of the 1096 cm1 absorption of CH3OCH3, but the large blue shift suggests the presence of a different functional group. Accordingly, we assign the 3030
dx.doi.org/10.1021/jp2018692 |J. Phys. Chem. A 2011, 115, 3029–3033
The Journal of Physical Chemistry A
ARTICLE
Table 1. Observed Argon Matrix and Density Functional Theory Calculated Infrared Absorptions (cm1) and Intensities (km/ mol, in parentheses) for the CH3OCH2 Radicala CH3OCH2
CD3OCD2 calcd
obsd
BPW91
obsd
B3LYP
BPW91
mode
3261.4 (11)
3201.6 (11)
2436.4 (7)
2391.5 (8)
CH2 antisym. CH str.
3133.7 (18)
3077.9 (17)
2322.8 (11)
2280.5 (10)
CH3 antisym. CH str
3108.3 (23) 3060.3 (49)
3047.7 (24) 2996.7 (52)
2246.9 (22) 2270.7 (29)
2202.8 (22) 2223.1 (30)
CH2 sym. CH str. CH3 antisym. CH str
3001.8 (58)
2936.7 (63)
2152.0 (40)
2105.2 (43)
CH3 sym. CH str.
1500.2 (18)
1456.6 (17)
1080.8 (1)
1048.0 (1)
CH3 deform.
1491.8 (4)
1445.0 (4)
1140.8 (40)
1101.4 (36)
CH3 deform. þ CH2 bend.
1485.9 (8)
1439.5 (8)
1073.8 (4)
1040.2 (4)
CH3 deform.
1454.3 (2)
1408.9 (1)
1066.3 (5)
1034.3 (4)
CH3 deform. þ CH2 bend.
1253.9
1280.7 (147)
1239.9 (123)
1286.7 (151)
1248.0 (124)
antisym. OCO str.
1226.6
1245.4 (35) 1165.4 (2)
1207.3 (30) 1126.1 (1)
837.6 (10) 901.2 (3)
815.6 (9) 871.4 (3)
1131.7 (8)
1098.6 (6)
1468.1
944.4
a
B3LYP
calcd
1123.0
1267.7
CH3 rock. CH3 rock. CH3 rock. þ CH2 in plane deform.
872.4 (7)
847.2 (8)
1040.2 (18)
1008.3 (15)
507.7 (60)
418.1 (31)
400.7 (33)
414.6 (4)
363.2 (4)
351.2 (4)
OCO bend.
292.2 (5)
288.2 (5)
224.8 (4)
221.4 (4)
CH2 twist
159.3 (3)
159.7 (3)
116.5 (2)
116.6 (2)
CH3 tors.
953.4 (38)
926.0 (36)
529.4 (59) 428.4 (4)
1033.3
sym. OCO str. CH2 out of plane wag.
Calculated using the 6-311þþG(d,p) basis: B3LYP and the larger 6-311þþG(3df,3pd) basis gave frequencies within 10 cm1.
four absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm1 to the CH3OCH2 radical containing a methylene substituent. The deuterium substituted product exhibits a quite different infrared spectrum due to the change of mode coupling with deuterium instead of hydrogen. In our CD3OCD3 experiment, only three weaker product absorptions at 1267.7, 1033.3, and 1123.0 cm1 were observed. The former two absorptions are probably due to the deuterium counterparts of the strongest 1253.9 and 944.4 cm1 COC skeletal stretching absorptions observed in the CH3OCH3 experiment. Assignment of the 1123.0 cm1 absorption will require insight from calculations. To support our experimental assignments, density functional theoretical calculations (B3LYP and BPW91) were carried out on the structure, vibrational frequencies, and infrared intensities of the CH3OCH2 radical. The optimized geometry of the radical is shown in Figure 4, which is in agreement with previous calculations for the doublet ground state.710,1316 As illustrated in Table 1, the calculated vibrational frequencies of the CH3OCH2 radical correlate well with the observed values and thus provide strong support for our experimental assignments. Harmonic B3LYP values are usually a few percent higher and BPW91 results closer to observed anharmonic frequencies.27 Frequency calculations at the B3LYP level of theory with anharmonicity included in the Gaussian 09 program are about 10 cm1 lower than the experimental values. Although five infrared absorptions with low to moderate intensities are predicted in the CH stretching region (anharmonic frequencies are 60130 cm1 lower than the harmonic values), no new absorption was observed throughout this region, which is probably due to the overlap with the strong precursor bands as well as poor signal-to-noise in the 3000 cm1 region. Since we did not observe any product absorption above 1500 cm1, and
Figure 4. Optimized structure (bond length in angstrom and bond angle in degree) and selected molecular orbitals for the CH3OCH2 radical computed at the B3LYP/6-311þþG(d,p) level of theory. The larger 6-311þþG(3df,3pd) basis set gave 0.0030.004 Å shorter bond lengths.
absorptions below 400 cm1 are out of our instrumental limits, we will focus on the frequencies ranging from 1500 to 400 cm1. Our calculations revealed that there are five absorptions with relatively high infrared intensities (>10 km/mol) in this region. The strongest band predicted at 1280.7 cm1 (B3LYP) is a mostly antisymmetric OCO vibration, which blue-shifted to 1286.7 cm1 upon deuterium substitution due to different coupling with CH3 and CD3 deformation modes. Following these calculated frequencies, the 1253.9 cm1 absorption observed in our experiment is assigned to the antisymmetric OCO stretch with its deuterium counterpart at 1267.7 cm1. The 13.8 cm1 difference between H and D isotopic bands is consistent with the shift of 68 cm1 predicted by our calculations. The symmetric OCO stretching 3031
dx.doi.org/10.1021/jp2018692 |J. Phys. Chem. A 2011, 115, 3029–3033
The Journal of Physical Chemistry A vibration is calculated at 953.4 cm1 (B3LYP) with more participation of hydrogen atoms. As a result, this band possesses a large blue shift (86.8 cm1) when the hydrogen atoms are replaced by deuterium atoms. Experimentally, the 944.4 cm1 absorption is assigned to the mostly symmetric OCO stretching vibrational mode, and the weak 1033.3 cm1 absorption in the CD3OCD3 experiment is attributed to its deuterium counterpart. The experimental H/D shift (88.9 cm1) is in excellent agreement with our theoretical predictions. The two infrared absorptions at 1468.1 and 1226.6 cm1 are assigned to deformation and rocking modes involving both CH3 and CH2 groups on the basis of the frequencies calculated at 1500.2 and 1245.4 cm1. Calculated deuterium isotopic substitution revealed that these two frequencies shift to 1080.8 and 837.6 cm1, respectively. The rather low infrared intensity of the 1080.8 cm1 absorption (Table 1) results in the absence of this band in our CD3OCD3 experiment while the 837.6 cm1 absorption is probably masked by the strong CD3OCD3 band in the same region. The 1123.0 cm1 absorption present in the CD3OCD3 experiment corresponds to the calculated absorption at 1140.8 cm1 (B3LYP), which is a mixed mode of CD3 deformation and CD2 bending. The hydrogen counterpart of this band was predicted to be very weak, and it is not observed here. In addition to the above-mentioned absorptions, a band calculated at 529.4 cm1 for the out-of-plane CH2 wagging mode was predicted to have moderate intensity. However, we did not observe any absorption in this region. The infrared intensity of this band is often overestimated, which probably accounts for the experimental absence. Finally, the good correlation between experimental and theoretical vibrational frequencies provides solid evidence for our assignment of the CH3OCH2 radical. Such agreement is expected for B3LYP and BPW91 density functional calculated and observed vibrational frequencies.27 Our DFT calculations revealed that the two CO bonds in the CH3OCH2 radical are different due to the loss of one hydrogen atom, which is consistent with previous computations.710,1316 As shown in Figure 4, the H3CO bond length is 1.424 Å (B3LYP values given), about the same (1.413 Å) as calculated at the same level of theory for DME itself and measured in the microwave spectrum (1.410 ( 0.003 Å).28 Structural parameters calculated by the BPW91 functional are almost the same (within 0.01 Å) as those from B3LYP calculations. The OCH2 bond length is calculated to be 0.07 Å shorter than the H3CO bond length in this radical, which suggests that the CO bonding interactions are different in the two CO bonds. In order to get more detailed insight into bonding in the radical, selected frontier orbitals are illustrated in Figure 4. For the OCH2 moiety, the C 2p orbital with one unpaired electron overlaps with one of the O 2p orbitals occupied by lone pair electrons to form a doubly occupied π bonding orbital (SOMO-2) and a singly occupied π antibonding orbital (SOMO). The net π bond order is 0.5, which shows that there are π bonding interactions between the oxygen atom and the CH2 group. Due to these additional interactions, the OCH2 bond is strengthened compared with the H3CO bond, which contains only a single CO σ bond. Evidence for the formation of the new π bond can be also derived from the geometry of the OCH2 moiety. The sum of one HCH and two OCH bond angles is 354.4°, suggesting only slight distortion of the OCH2 moiety from the planar geometry. The CH3OCH2 radical was produced on sample deposition with laser ablation of metal targets. The focused, pulsed laser creates a bright plume on the metal surface, and this light can perform photochemistry on the depositing matrix sample. Here this process involves CH bond dissociation by vacuum-UV radiation in the
ARTICLE
ablation plume20 reaction (1) as concluded for CH3 radical formed in similar methane experiments.29 This dissociation reaction was found to be endothermic by about 90 kcal/mol from previous theoretical studies.810,16 CH3 OCH3 þ vacuum-UV f CH3 OCH2 þ H
ð1Þ
The radical absorptions decreased on annealing and on irradiation with near-UV wavelengths. Our wavelength-dependent irradiation revealed that the radical absorptions remained unchanged upon λ > 290 nm irradiation but decreased markedly when the sample was subjected to broad band irradiation (λ > 220 nm). Hence the formation of the CH3OCH2 radical requires higher energy photons (λ < 220 nm). Earlier studies on the decomposition kinetics of DME revealed that the hydrogen abstraction reaction is kinetically hindered by an energy barrier of 95.5 kcal/mol,30 which is lower in energy than many UV photons produced by laser ablation of the metal target. Since DME has a series of absorptions in the region below 220 nm, these excited states of DME are involved in producing the CH3OCH2 radical.31 Note that the absorption of the diatomic UH molecule increased on annealing due to the reaction of uranium and hydrogen atoms in laser ablation experiments with the U metal target. Hydrogen atoms are expected to be present in the matrix along with the formation of the CH3OCH2 radical during sample deposition, reaction 1. The decomposition mechanism of CH3OCH2 radical has been the subject of several experimental and theoretical studies due to its important role in combustion and atmospheric processes.4a,8,9,14,15,32,33 The formation of formaldehyde and CH3 radical was proposed to be the major decomposition channel of CH3OCH2 radical in the gas phase. However, our experimental observations suggested a different decomposition mechanism for CH3OCH2 radical in solid argon, which resulted in the formation of HCO and CH4 (Figure 2). No change was found in the formaldehyde absorption, and we did not observe any new band in the region of methyl radical absorption.29 According to previous high level ab initio calculations, the formation of HCO and CH4 was thermodynamically favored by about 16.5 kcal/mol over that of H2CO and CH3, and the conversion from the former two molecules to the latter ones was kinetically hindered by an energy barrier around 12 kcal/mol.15 These values are in qualitative agreement with the experimental data.34,35 Note that this calculated energy barrier is less than the available energy (more than 20 kcal/mol) released with the formation of H2CO and CH3 molecules from the proposed (CH3OCH2) transition state.15 As a result, these two molecules trapped in the same matrix cage are not stabilized, and they can undergo intermolecular reaction to form the more stable HCO and CH4 molecules as the final reaction products. In the gas phase, the initially formed more energetic H2CO and CH3 products separate from each other, which prevents them from further intermolecular reactions. In the CD3OCD3 experiment, the CD3OCD2 radical absorptions were also observed on deposition but their infrared intensities were weaker than those in the experiment with CH3OCH3 sample. Since formation of the CD3OCD2 radical requires breaking the CD bond, the kinetic isotope effect should be responsible for the relative low yield of the radical product in the deuterium-substituted precursor experiment. The CD3OCD2 radical absorptions were destroyed on broad band irradiation with a slight increase for the DCO absorption. Almost no increase was found for CD4 absorption, which is probably due to the multiple site splits of the broad CD4 absorption. 3032
dx.doi.org/10.1021/jp2018692 |J. Phys. Chem. A 2011, 115, 3029–3033
The Journal of Physical Chemistry A Hence, the deuteriated radical photodecomposition pathway is probably the same in the matrix as for the hydrogenic species.
’ CONCLUSIONS We have prepared and trapped the methoxymethyl radical, CH3OCH2, from laser-excited metal plume irradiation of DME during condensation in excess argon. The CH3OCH2 radical is characterized by the four strongest infrared absorptions, deuterium substitution, and theoretical calculations. The two CO bond lengths in this radical are different due to the presence of additional π bonding interactions in the OCH2 bond. UV irradiation destroys the CH3OCH2 radical, and the HCO and CH4 molecules are produced. The decomposition mechanism of the CH3OCH2 radical in solid argon is different from that in the gas phase, where formaldehyde and methyl radical are proposed to be the decomposition products. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT We gratefully acknowledge financial support from DOE Grant No. DE-SC0001034 and NCSA computing Grant No. CHE070004N. ’ REFERENCES (1) Kohse-H€oinghaus, K.; Oβwald, P.; Cool, T. A.; Kasper, T.; Hansen, N.; Qi, F.; Westbrook, C. K.; Westmoreland, P. R. Angew. Chem., Int. Ed. 2010, 49, 3572. (2) Curran, H. J.; Fischer, S. L.; Dryer, F. L. Int. J. Chem. Kinet. 2000, 32, 741. (3) Eskola, A. J.; Carr, S. A.; Blitz, M. A.; Pilling, M. J.; Seakins, P. W. Chem. Phys. Lett. 2010, 487, 45. (4) (a) Sehested, J.; Sehested, K.; Platz, J.; Egsgaard, H.; Nielsen, O. J. Int. J. Chem. Kinet. 1997, 29, 627. (b) Sehested, J.; Møgelberg, T.; Wallington, T. J.; Kaiser, E. W.; Nielsen, O. J. J. Phys. Chem. 1996, 100, 17218. (5) Rosado-Reyes, C. M.; Francisco, J. S.; Szente, J. J.; Maricq, M. M.; Østergaard, L. F. J. Phys. Chem. A 2005, 109, 10940. (6) Maricq, M. M.; Szente, J. J.; Hybl, J. D. J. Phys. Chem. A 1997, 101, 5155. (7) Song, X.; Hou, H.; Wang, B. Phys. Chem. Chem. Phys. 2005, 7, 3980. (8) Pan, Y. X.; Liu, C. J. Fuel Process. Technol. 2007, 88, 967. (9) Good, D. A.; Francisco, J. S. J. Phys. Chem. A 2000, 104, 1171. (10) Curran, H. J.; Pitz, W. J.; Westbrook, C. K.; Dagaut, P.; Boettner, J. C.; Cathonnet, M. Int. J. Chem. Kinet. 1998, 30, 229. (11) Langer, S.; Ljungstroem, E.; Ellermann, T.; Nielsen, O. J.; Sehested, J. Chem. Phys. Lett. 1995, 240, 53. (12) Liu, R.; Maricq, M. M.; Li, Y.; Francisco, J. S. J. Chem. Phys. 1999, 110, 4410. (13) (a) El-Nahas, A. M.; Uchimaru, T.; Sugie, M.; Tokuhashi, K.; Sekiya, A. THEOCHEM 2005, 722, 9. (b) Bottoni, A.; Casa, P. D.; Poggi, G. THEOCHEM 2001, 542, 123. (14) Li, Q. S.; Zhang, Y.; Zhang, S. J. Phys. Chem. A 2004, 108, 2014. (15) Liu, J. Y.; Li, Z. S.; Wu, J. Y.; Wei, Z. G.; Zhang, G.; Sun, C. C. J. Chem. Phys. 2003, 119, 7214. (16) Nash, J. J.; Francisco, J. S. J. Phys. Chem. A 1998, 102, 236. (17) (a) Jacox, M. E. Annu. Rev. Phys. Chem. 2010, 61, 1. (b) Jacox, M. E. Acc. Chem. Res. 2004, 37, 727. (c) Jacox, M. E. Chem. Soc. Rev. 2002, 31, 108.
ARTICLE
(18) Wrobel, R.; Sander, W.; Kraka, E.; Cremer, D. J. Phys. Chem. A 1999, 103, 3693. (19) (a) Andrews, L. Chem. Soc. Rev. 2004, 33, 123. (b) Andrews, L.; Citra, A. Chem. Rev. 2002, 102, 885.(c) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040 (Review article). (20) (a) Zhou, M. F.; Andrews, L.; Bauschlicher, C. W., Jr. Chem. Rev. 2001, 101, 1931. (b) Andrews, L.; Kushto, G. P.; Zhou, M. F.; Willson, S. P.; Souter, P. F. J. Chem. Phys. 1999, 110, 4457.(c) Flesch, R.; Schurmann, M. C.; Hunnekuhl, M.; Meiss, H.; Plenge, J.; Ruhl, E. Rev. Sci. Instrum. 2000, 71, 1319 and references therein (Extreme Ultraviolet Laser-Produced-Plasma Radiation). (21) Frisch, M. J.; et al. Gaussian 09, Revision B.01; Gaussian, Inc.: Wallingford, CT, 2010. (22) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (23) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Perdew, J. P.; Burke, K.; Wang, Y. Phys. Rev. B 1996, 54, 16533. (24) (a) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639. (b) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650. (25) Milligan, D. E.; Jacox, M. E. J. Chem. Phys. 1969, 51, 277. (26) (a) Souter, P. F.; Kushto, G. P.; Andrews, L.; Neurock, M. J. Am. Chem. Soc. 1997, 119, 1682. (b) Raab, J.; Lindh, R. H.; Wang, X.; Andrews, L.; Gagliardi, L. J. Phys. Chem. A 2007, 111, 6383. (27) (a) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502. (b) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 2937. (28) Blukis, U.; Kasai, P. H.; Myers, R. J. J. Chem. Phys. 1963, 38, 2753. (29) (a) Andrews, L.; Cho, H.-G. J. Phys. Chem. A 2005, 109, 6796. (b) Jacox, M. E. J. Mol. Spectrosc. 1977, 66, 272. (30) Loucks, L. F.; Laidler, K. J. Can. J. Chem. 1967, 45, 2763. (31) Bremner, L. J.; Curtis, M. G.; Walker, I. C. J. Chem. Soc., Faraday Trans 1991, 87, 1049. (32) Loucks, L. F.; Laidler, K. J. Can. J. Chem. 1967, 45, 2767. (33) Zhao, Z.; Chaos, M.; Kazakov, A.; Dryer, F. L. Int. J. Chem. Kinet. 2008, 40, 1. (34) Aronowitz, D.; Naegeli, D. Int. J. Chem. Kinet. 1977, 9, 471. (35) Hidaka, Y.; Sato, K.; Yamane, M. Combust. Flame 2000, 123, 1.
3033
dx.doi.org/10.1021/jp2018692 |J. Phys. Chem. A 2011, 115, 3029–3033
