theoretical study of the low-lying excited states of butoxy radicals and non-radiative decay routes

Chinese Journal of Chemistry, 2007, 25, 1467—1473 Full Paper

* E-mail: [email protected], [email protected]; Fax: 0086-010-58802075 Received January 18, 2007; revised April 23, 2007; accepted June 18, 2007. Project supported by the National Natural Science Foundation of China (Nos. 20472011, 20673013), the Scientific Research Foundation for the

Returned Overseas Chinese Scholars by State Education Ministry and the Major State Basic Research Development Program (No. 2004CB719903).

© 2007 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Theoretical Study of the Low-Lying Excited States of Butoxy Radicals and Non-Radiative Decay Routes

LIN, Ling(林玲) ZU, Li-Li*(祖莉莉) FANG, Wei-Hai*(方维海) YU, Jian-Guo(于建国) LIU, Ruo-Zhuang(刘若庄)

Department of Chemistry, Beijing Normal University, Beijing 100875, China

The potential energy surfaces for the butoxy radical dissociation into R•＋O on the six low-lying electronic states have been determined with the combined CASSCF and MR-CI methods. The isomerization reactions between the different conformers of 1- and 2-butoxy radicals at the X� and B� states have been also investigated with the MP2, B3LYP, and CASSCF methods. The non-radiative decay mechanisms of butoxy radicals at the B� state have been characterized with the computed potential energy surfaces and intersections. Supported by recent LIF experi-mental results, it was predicted that the t-butoxy radical would predissociate via the /B C�� intersection. As to 1- and 2-butoxy radicals, the relative energies of the transition states for the isomerization reactions between conform-ers at the B� state are much lower than those of the /B C�� intersections, resulting in the predominance of the isomerization in the decay of the B� state for 1- and 2-butoxy radicals.

Keywords butoxy radicals, excited states, non-radiative decay, Botential energy profile

Introduction

Alkoxy radicals are key intermediates in the atmos-pheric oxidation of organic compounds.1 The fate of alkoxy radicals in the atmosphere influences the yield of ozone, air toxicants and organic aerosol in the polluted air.2 For methoxy radical, the smallest member in alkoxy groups, extensive studies3-12 have been per-formed. The X B−� �

electronic transition of methoxy radical was revealed to be the excitation of an electron from the C—O σ orbital to the half filled p-π orbital localized on the oxygen atom by Foster and his co-workers.5 Jackels6 investigated the potential energy sur-face of the methoxy radical and suggested a quenching path through predissociation, which was supported by the LIF lifetime measurements.7 However, although having a similar lifetime behavior, a photodissociation dynamics study of ethoxy radical by Choi et al.13 pro-posed a dissociation mechanism in which the excited ethoxy radical isomerized through excited states of ei-ther the 1- or 2-hydroxyethyl radicals and then dissoci-ated to C2H3＋H2O. In the meantime, studies about the non-radiative mechanism for the excited states of larger alkoxy radicals are sparse.

In the present work, butoxy radicals are taken as examples to explore the properties of the excited states and the non-radiative mechanisms of the alkoxy radicals. According to the location of the oxygen bond, three structure isomers for the butoxy radicals, namely 1-butoxy, 2-butoxy and t-butoxy are discussed. For the

open chain isomers, 1-butoxy has five possible con-formers, and 2-butoxy has three conformers (Figure 1). The moderate resolution LIF spectra of 1-, 2-, and t-butoxy radicals in the supersonic jet14-16 have been obtained (Figure 2), showing very different spectro-scopic patterns for different structural isomers. From Figure 2 one can see that the chain alkoxy radicals dis-play a short expanding spectrum while the most branched isomer (t-butoxy) exhibits a rich spectrum with long vibration progression, suggesting different non-radiative decay paths for the different butoxy iso-mers. Assignment of rotational resolved electronic spectra of the 1-butoxy and 2-butoxy radicals15,16 re-vealed that multiple conformers co-existed in the su-personic jet non-equilibrium condition. In the spectrum of the 1-butoxy radical, 6 bands were assigned to 3 of the total 5 conformers,15 while 5 strong bands were as-signed to 3 of the total 3 conformers in the 2-butoxy spectrum.16 At most ν'＝1 vibrational band was ob-served for each conformer of the 1- and 2-butoxy radi-cals. In contrast, up to ν'＝7 C—O stretching vibration bands were observed in the t-butoxy spectrum.14

A large number of studies have been carried out about the LIF spectra for alkoxy radicals, but the theo-retical calculations are quite less, especially for the bu-toxy radicals. Almost all of the theoretical investigations about butoxy radicals were focused on the isomerization and decomposition reactions at the ground state.17-21 Due to the near-degenerated ground state, and the ab-sence of the π-electron system, it would be very difficult

1468 Chin. J. Chem., 2007, Vol. 25, No. 10 LIN et al.


Figure 1 Structures of butoxy radicals: (1) three isomers of butoxy radicals; (2) five unique conformers of 1-butoxy radical; (3) three unique conformers of 2-butoxy radical.

Figure 2 Laser-induced fluorescence excitation spectra of (a) 1-butoxy, (b) 2-butoxy and (c) t-butoxy in supersonic jet. Detail assignment of the vibrational bands can be referred to Ref. 14—16 and 25.

to study its excited states theoretically. To our knowl-edge, there has been no report that involves ab initio studies on the properties of the excited states for the butoxy radicals yet. In the present work, we explored the potential energy surfaces of the six low-lying states for the butoxy radicals with the advanced ab initio methods, which would provide new insights into the

non-radiative mechanism for the butoxy radicals at the excited states and would be helpful to understand the photochemical behavior for even larger alkoxy radicals.

Computation methods

Several low-lying electronic states of the butoxy radicals have been studied with various quantum chemical techniques. The stationary structures of the butoxy radicals at the ground state were optimized with the B3LYP, MP2, and CASSCF methods. But only the CASSCF method was used to optimize the structures at the excited states. The 6-31＋G** basis set was used for structural optimization. Once convergence on the ge-ometry optimization had been reached, the harmonic frequency was examined to confirm the optimized ge-ometry to be a true minimum or first-order saddle point. The state-averaged (SA) CASSCF method was used to determine the geometries of the lowest intersection for each conformer. To refine the relative energies, the sin-gle-point energy was calculated with the MR-CI method for the CASSCF optimized stationary structures.

The choosing of the active space is crucial for CASSCF calculation. In the present work, we chose an active space of 9 electrons distributed in 7 orbitals [hereafter referred to as CAS(9,7)], involving the non-bonding orbitals of the O atom, the σ and σ* orbi-tals of the C—O bond. The other active orbitals and

Butoxy radicals Chin. J. Chem., 2007 Vol. 25 No. 10 1469


electrons were chosen by the program automatically. To describe the C—O bond dissociation of the bu-

toxy radicals, the potential energy profiles of the six low-lying electronic states were scanned with the CASSCF method and 6-31G* basis set. The single-point energy was calculated with the MR-CI method. The C—O distance was elongated from 0.12 nm to 0.34 nm with a step size of 0.02 nm, while other bond parameters were fixed at the optimized X� structure.

In the present work, all the MP2 and B3LYP calcu-lations have been carried out with the Gaussian 03,22 while the CASSCF and MR-CI calculations were per-formed with the MOLPRO package of programs.23

Results and discussion

t-Butoxy isomer

At the ground state, the t-butoxy radical has only one unique conformer, and the highest symmetry it can maintain is Cs symmetry, while the structure with C1 symmetry was always obtained when it was optimized without the symmetry being restricted to Cs. And further more, a low-lying state 2A A� was found in our calcula-tion, stating that the Jahn-Teller effect causes the sepa-ration of degenerate ground state due to the reduction of the symmetry. This is consistent with the experimental observation24 that a weaker progression was found to originate from a wavenumber ca. 312 cm－1 higher than that the C—O progression originated from.

The properties of the six low-lying electronic states of the t-butoxy radical have been explored and the four frontier molecular orbitals are plotted in Figure 3. Thereinto, the HOMO and HOMO-1 are both the non-bonding orbitals that are mainly localized on the O atom, in which the HOMO is half filled. The HOMO-2 and LUMO are σ(C—O) and σ*(C—O) orbitals in nature, respectively. Upon inspecting the coefficients of configuration functions of the MR-CI wave functions and the related molecular orbitals, the characteristics of the six low-lying states become very clear. The ground state is labeled as 2X A� , and the HOMO is half-filled, as mentioned above. The first excited electronic state ( 2A A� ) originates mainly from one electron transition from the occupied (HOMO-1) to the single occupied (HOMO) nonbonding orbital of the O atom. That is, the only difference between the A� and X� states is the different orientation of the half-filled O p-π orbital. The second excited state ( 2B A� ) was confirmed to be of 2σp character, which corresponds to the promotion of one electron from the σ orbital of the C—O bond (HOMO-2) to the HOMO. The 4D A� state arises from one electron transition from the σ (HOMO-2) to the σ* (LUMO) of the C—O bond. As for 4C A�

and 2E A�

states, both of them correspond to one electron promotion from the occupied p-π orbital of the O atom (HOMO-1) to the σ* orbital of the C—O bond (LUMO), except that the spin of the unpaired electrons is different. Of all these states,

Figure 3 Plots of the four frontier orbitals labeled by HOMO-2, HOMO-1, HOMO, and LUMO for the t-butoxy radical.

the C� and D� states are quadralet, while the others ( X� , A� , B� , and E� ) are doublet.

The potential energy surface of the six low-lying states for the t-butoxy radical is plotted in Figure 4, from which one can easily find that the surface of the A state resembles that of X� except that the former is a little higher in energy, in good agreement with the ex-perimental result.24 For the B� profile, there exists a minimum near 0.16 nm of the C—O bond. The C� , D� , and E� are all repulsive states, and the surfaces of them will intercross with that of B� state between 0.20—0.22 nm of the C—O bond. The profiles of C� and D�

states are very close and almost intercross with B� state at the same C—O bond length. Of the three conical intersections on the B� surface, /B C�� is the lowest in energy, which was presumed to be most likely to play an important role in the non-radiative mechanism for the t-butoxy radical. Accordingly, we are more interested in /B C�� than in other intersections.

Figure 4 Schematic potential energy profiles of the six low-lying electronic states for the t-butoxy radical, together with the relative energies calculated at the level of MR-CI/6-31G*.



We have carried out a full optimization for the X� and B� states at the level of CAS(9,7)/6-31＋G**. At the ground state, the length of the C—O bond was pre-dicted to be 0.143 nm, which is elongated to 0.169 nm at the B� state. The reason is that the B� state derives from one electron promotion from the C—O σ orbital to the half-filled p-π orbital of the O atom, resulting in the partial rupture of the C—O bond. By the MR-CI sin-gle-point energy correction, the adiabatic excitation en-ergy from X� to B� state was predicted to be 325 kJ/mol, which was reduced to 315 kJ/mol after the Davidson correction (as shown in Table 1), and agrees with the experimental result 309 kJ/mol (25866 cm－1)24 pretty well.

Table 1 Relative energies (in kJ/mol) of the B� and /B C�� for the 1-butoxy, 2-butoxy and t-butoxy radicals calculated using the combined CAS(9,7)/6-31＋G** and MR-CI methods including the Davidson correction.

Eexpt15,16,24 Ecalc(Davidson correction)

Isomers Conformers X� - B� X� - B� X� - /B C�� B� - /B C��

G1T2 343 351 421 69.0

T1T2 348 363 427 64.0

T1G2 349 361 417 60.2

G1G2 351 423 71.1

1-butoxy

G1′G2 352 421 68.6

G＋ 320 326 394 68.6

T 324 333 386 65.7 2-butoxy

G– 320 326 395 69.5

t-butoxy 309 315 384 69.0

The C—O stretching frequency of the B� minimum

was predicted to be 559 cm－1 (6.69 kJ/mol) (all of the calculated frequencies given in this paper are unscaled). The experimental spectrum shows that the average vi-brational band interval between the ν'C — O＝ n and ν'C—O＝n＋1 (0≤n≤6) levels is 521 cm－1 (6.23 kJ/mol) for the B� state.24,25 Obviously, our calculation agrees well with the result from the experiment.

The potential energy surface of the methoxy radical has been studied extensively and the mechanism of its photochemistry7-10 is well recognized at present. Our calculation indicates that the potential energy surface of the t-butoxy radical has a similar trend to that of the methoxy radical.6,9 One big difference between them is that the relative energy of the B� state with respect to the X� state was predicted to be 315 kJ/mol for t-butoxy radical, while the counterpart state of methoxy radical has the relative energy of 377 kJ/mol (31540 cm－1),5 which is a little higher than the dissociation limit 368 kJ/mol (3.81 eV)9 of the C—O bond at the ground state. As for the t-butoxy radical, the relative energy of the R•＋O with respect to the reactant was predicted to be 343 kJ/mol with the Davidson correction

at the ground state. So the minimum of B� state of t-butoxy will descend below the C—O dissociation limit (Figure 4).

The /B C�� intersection of t-butoxy was determined, and the significant change in the structure is associated with the C—O bond length, which was predicted to be 0.216 nm. It is elongated by 0.047 nm compared with that of B� . Relative to the B� minimum, the /B C�� intersection has an energy of 82.8 kJ/mol at the MR-CI level, and it was reduced to 69.0 kJ/mol with the Davidson correction (Table 1), which corresponds to the ν'C—O＝11 level. This is consistent with the experimen-tal lifetime measurements that the t-butoxy radical would not be strongly predissociated in the ν'＝0—7 levels.24,25 Emission has not been observed from the higher vibrational levels, allowing for the possibility that they maybe shortly lived.

Due to the observation that the fluorescence charac-ter of t-butoxy is similar to that of the CH3O radical, and the calculation result that /B C�� intersection of t-butoxy is close to the highest observed CO vibration level (ν'C—O＝7), it was presumed that the non-radiative mechanism for the t-butoxy radical may be the same as that of the methoxy radical. That is, the B� state of the t-butoxy radical will predissociate via the /B C�� inter-section and produce (CH3)3C•＋O(3P) at the ground state, causing the missing of the fluorescence at the higher CO vibrational level.

1-Butoxy isomer

Unlike the t-butoxy isomer, 1-butoxy has five unique conformers. Our calculation found that the relative en-ergies of the five conformers at the ground state were very close to one another, and the biggest difference in energy among them was less than 8.4 kJ/mol at the dif-ferent calculation levels. We investigated the isomeriza-tion reaction among the five conformers by optimizing the corresponding transition states. The relative energies of them are shown in Figure 5(a). For convenient com-parison, the labeling of the different conformers is con-sistent with the previous experimental papers.15,16,25 At the MP2/6-31＋G** level, the barriers for the isomeri-zation were predicted to be between 8.8—14.6 kJ/mol, which are much lower than the 1,5-H transfer barriers (ca. 38 kJ/mol17). So the isomerization among the dif-ferent conformers is easier to take place at the ground state.

Generally, a barrier higher than 21 kJ/mol is suffi-cient to suppress the isomerization between the isomers at room temperature,26 thus the 1-butoxy radical should exist in the most stable conformer at equilibrium. But under the condition of the supersonic-jet, the alkoxy radicals were generated by photolysis of alkylnitrite, the conformers of alkoxy radicals could be populated by photolysis laser energy and freezed in the fast cooling. Therefore, all of the conformers can exist contemporar-ily at the ground state in non-equilibrium condition.15



Figure 5 The potential energy surfaces of the isomerization between different conformers at the X� and B� states with the relative energies coming from MP2/6-31＋G** and MR-CI/ 6-31＋G** (with Davidson correction) respectively: (a) 1-butoxy radical and (b) 2-butoxy radical.

When the five conformers were excited to the B� state, the C—O bonds of them were all elongated to about 0.164 nm, which is a little shorter than that of the t-butoxy radical (0.169 nm). The MR-CI/6-31＋G** calculations with the Davidson correction predicted that the adiabatic excitation energy values from the X� to B� state for the G1T2, T1T2 and T1G2 conformers were 351, 363 and 361 kJ/mol respectively, which agree well with the experimental results 343, 348 and 349 kJ/mol.25 The relative energies of the B� state with respect to X� for the G1G2 and G1′G2 conformers were predicted

to be 351 and 352 kJ/mol, respectively, at the same cal-culation level. The experimental studies have not come out with the corresponding values for them so far. As it has been mentioned before, the relative energy of B� with respect to X� for the t-butoxy radical was pre-dicted to be 315 kJ/mol, which is pretty lower than those of the 1-butoxy radicals. On the other hand, our studies show the properties of the six low-lying states of 1-butoxy radical, and the resulting potential energy sur-face is similar to that of t-butoxy.

There are also possibilities for isomerization among the five conformers of 1-butoxy at the B� state, and we have optimized the corresponding transition states [Fig-

ure 5(a)]. All of the barriers are between 7.5—21 kJ/mol with Davidson correction. There are several reports17-21 concerning the H transfer reactions for butoxy radicals. The barrier of the 1,5-H transfer for 1-butoxy was pre-dicted to be about 38 kJ/mol at the ground state,17,19 which was predicted to be even higher at the B� state due to the excitation of one electron from the σ(C—O) to the half-filled p-π orbital of the O atom. So they would play a minor role in the non-radiative decay for the B� state of the 1-butoxy radical, while the isomeri-zation among the conformers would be much more im-portant.

In the studies of the isomerization between the dif-ferent conformers at the B� state, the barrier for T1G2 to transform into G1G2 and G1′G2 were predicted to be 7.5 and 9.6 kJ/mol respectively, that is, when the excess energy is less than 7.5 kJ/mol for T1G2, the fluorescence will be predominant, while the isomerization will play an important role when the excess energy is above 7.5 kJ/mol. Our calculation predicted that the frequency of the C—O vibration for T1G2 at B� minimum was 696 cm－1 (8.3 kJ/mol), which is higher than the lower bar-rier (7.5 kJ/mol), as accounts for the fact that the band of C—O vibration was not observed in the experi-ment.15 While the T1T2 conformer was concerned, in the LIF experimental spectrum, two bands of 169 cm－1 (2.0 kJ/mol) and 671 cm－1 (8.0 kJ/mol) above the origin were assigned to the CCO backbone deformation and the C—O vibration.15 In our calculations, the frequen-cies of the two corresponding motions were predicted to be 185 cm－1 (2.2 kJ/mol) and 697 cm－1 (8.3 kJ/mol) respectively, which agree well with the experimental results. The barrier for T1T2 to transform into G1T2 was predicted to be 9.6 kJ/mol, which is higher than the C—O vibration frequency, so that the band of C—O stretch-ing could be observed. As for the G1T2 conformer, things were predicted to be similar to T1T2 by our cal-culation, but they were not supported by the experiment. It was presumed that more bands would be observed for G1T2 experimentally if techniques with higher sensitiv-ity and resolution were employed. The G1G2 and G1′G2 conformers would also be observed, for we found that the energies of the B� relative to X� state for the G1T2, G1G2 and G1′G2 conformers were almost the same (351, 351 and 352 kJ/mol, respectively). On the other hand, distinguishing them experimentally would be difficult since the band origins of them would be pretty close to one another and even overlap.

The /B C�� intersections were found for all of the conformers of the 1-butoxy radical except for T1G2, which has an avoided intersection /B C�� in our study. The C—O bonds of the structures for /B C�� intersec-tions are elongated to about 0.207 nm for each con-former (0.203 nm for T1G2) and already broken up. The relative energies of them are listed in the Table 1, from which we can easily find that the energies of the four

/B C�� intersections are close to one another, and the



energy of the avoided intersection /B C�� for T1G2 is a little lower, but this will not make a difference, and for all of the /B C�� were far away from the observed vi-brational levels (ν'CO＝1 or 0), they were presumed to influence the non-radiative mechanism of 1-butoxy radical little. In this case, the isomerization between any two of the five conformers and the subsequent inter-conversion to the X� state were predicted to be the dominant processes for the decay of the 1-butoxy radi-cal at the B� state. Then the radical might possibly un-dergo the decomposition and the isomerization at the ground state.

2-Butoxy isomer

There are three conformers for the 2-butoxy radical and the energies of them are close to one another at the ground state. The biggest energy difference between the conformers was predicted to be less than 4.6 kJ/mol in our calculation. Two transition states for the isomeriza-tions among them were found at the X� state and the relative energies of them are shown in Figure 5(b). At the level of MP2/6-31＋G**, the barriers of the trans-formations from T and G– to G＋ were predicted to be 10.9 and 14.6 kJ/mol, respectively, which are a little higher than those of the isomerizations for the 1-butoxy radical, and it was predicted that this was attributed to the bigger steric hindrance in the 2-butoxy radical.

When the 2-butoxy radical is excited to the B� state, its structure will also change. The C—O bond for the three conformers will be elongated to about 0.167 nm, which is between the corresponding values for the B� structures of the t-butoxy (0.169 nm) and 1-butoxy radical (ca. 0.164 nm). We studied the properties of the six low-lying states for the 2-butoxy radical, and it turned out that its potential energy surface of the six low-lying states was similar to those for t-butoxy and 1-butoxy radicals, and the characteristics of the states were also the same.

The adiabatic excitation energies from the X� to B� state for the G＋, T, and G–

conformers were pre-dicted to be 336, 342 and 336 kJ/mol respectively, at the MR-CI/6-31＋G** level. After the Davidson correction, they became 326, 333 and 326 kJ/mol, which agree well with the experimental results 320, 324 and 320 kJ/mol,16,25 respectively (see Table 1).

We also investigated the isomerization reactions between any two of the three conformers at the B� state and the relative energies of the transition states were shown in Figure 5(b). All of the barriers were pre-dicted to be between 8.8—24.7 kJ/mol with the David-son correction. Take T as an example, the barrier for transformation from T to G＋ was predicted to be 8.8 kJ/mol. The frequency of C—O stretching of the T con-former at the B� minimum was calculated to be 650 cm－1 (7.8 kJ/mol), which agrees well with the experi-mental result 7.3 kJ/mol (610 cm－1).6 Obviously, the energy of the C—O vibration is below the isomerization

barrier, corresponding to the observation of the band of C—O vibration. Things are similar to the G＋ con-former. It was presumed that more bands for T, G＋ and G– should be observed while the experimental tech-niques were improved.

We also located the /B C�� intersections for the three conformers, and the changing trend of the struc-tures is similar to those of the t- and 1-butoxy radicals. The C—O bond of the /B C�� for each of the conformer is elongated to about 0.213 nm, which is between the corresponding value for the 1-butoxy (0.216 nm) and t-butoxy radicals (0.208 nm). The relative energies of the /B C�� intersections for the 2-butoxy radical are listed in Table 1. Similar to the 1-butoxy radical, the

/B C�� intersections of the conformers of the 2-butoxy radical are far higher than the observed highest vibration level (ν'CO＝1) in the fluorescence spectrum. So we as-sumed that the non-radiative decay path via the pre-dissociation mechanism through the /B C�� inter-section could be ruled out for the 2-butoxy radical and a similar mechanism as the 1-butoxy radical was pre-dicted for the 2-butoxy radical.

Conclusion

Due to the similarity of the fluorescence character for the t-butoxy and the methoxy radicals in experiment, and the moderate energy of the /B C�� intersection for the t-butoxy radical, the non-radiative decay mechanism of the t-butoxy radical was predicted to be similar as that of CH3O radical. That is, the B� state of t-butoxy radical would predissociate via the /B C��

intersection, resulting in the missing of the fluorescence at the higher vibrational levels (ν'CO＞7). However, there is another possible non-radiative decay route for the t-butoxy radical. As it has been mentioned before, the potential well of the B� state sinks in that of the X� state. The interconversion from B� to X� could take place via vibrational relaxation when the energy of the vibrational energy level was higher than the C—O dissociation limit and the t-butoxy radical would fragment into R•＋O(3P). Therefore, the fluorescence would not be ob-served at or above those vibrational energy levels. The dissociation energy of the ground state t-butoxy was predicted to be 343 kJ/mol, which is lower than the ob-served transition energy of ν'CO＝7 (353 kJ/mol). Hence, this route may play a minor role in the non-radiative decay mechanism of the t-butoxy.

As far as the 1-butoxy and 2-butoxy radicals were concerned, the /B C�� of them were far away from the observed vibrational levels (ν'CO＝1 or 0). Consequently, it was predicted that /B C�� intersection would not play an important role in the non-radiative decay mechanism. On the other hand, the isomerization barriers between any two of the conformers at the B� state are quite low, providing an effective non-radiative channel, thus sug-gests that the isomerizations at the B� state and the



subsequent interconversion to the X� state should be the main reason for the quenching of the fluorescence. Subsequently, it might undergo decomposition or isom-erization at the ground state. However, further experi-mental and theoretical studies are needed to understand the detail of the interconversion and the subsequent processes of the butoxy radicals.

Acknowledgment

The authors gratefully acknowledge helpful discus-sions with Professor Terry A Miller of Ohio State Uni-versity.

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(E0701181 ZHAO, X. J.; DONG, H. Z.)

theoretical study of the low-lying excited states of butoxy radicals and non-radiative decay routes

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