Article pubs.acs.org/JPCA
An ab Initio Investigation of Fluorobromo Carbene Erping Sun, Rui Li, Qixiang Sun, Changli Wei, Haifeng Xu,* and Bing Yan* Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China ABSTRACT: Fluorobromo carbene, an important halogenated carbene in the stratospheric ozone depletion, has long been received considerable interest. However, the energy, structure, and dynamics of even the lowest excited states have not been well understood. In this paper, we performed a detail ab initio study on CFBr using complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) method. We investigated the effect of basis set on the CASPT2 results of the ground X1A′ state and the first excited singlet A1A″ state. The potential energy surface (PES) of the A1A″ state along C−Br bond distance was carefully examined at CASPT2/cc-pV5Z level, by optimizing C−F bond and F−C−Br angle at every C−Br bond length in contrast to fix them at the equilibrium values. On the basis of the PES, a reliable barrier height of the A1A″ state was obtained from CASPT2 and MRCI+Q calculations with different basis sets, considering the scalar relativistic effect, spin−orbit coupling, and core−valence correlation. Finally, we carried out the first theoretical study on higher excited state with energy up to 7 eV. The present calculated results were compared with previous experimental and theoretical results where available. Our results will add some understanding and shed more light on the structure and dynamics of electronic states of CFBr radical.
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INTRODUCTION As important intermediates in various chemical reactions, carbenes have been received intense research interest with regard to their electronic structure and photochemistry. In particular, triatomic halogenated carbenes, CXY (X = H, F, Cl, Br, I; Y = F, Cl, Br, I), are viewed as model systems for understanding the spectroscopy, dynamics and chemistry of carbenes and have been widely studied both experimentally and theoretically (see the recent celebrated review and references therein).1 Due to the numerous interactions between the electronic states, such as Renner−Teller effect, spin−orbit coupling, avoided crossing, or nonadiabatic interaction leading to predissociation, the spectroscopy and photodissociation dynamics of halocarbenes are rather complicated, which stimulate scientists to continuously perform experimental and theoretical studies on these important reactive intermediates. During past several decades, with the advances of highresolution laser-based spectroscopic techniques along with theoretical methods, a variety of halocarbenes, including monohalogenated carbenes CHF2−5/CHCl6−10/CHBr11−13/ CHI,13 dihalogenated carbenes CCl2,14−17 CBr2,18 CFCl,19 CFBr,20−22 and CFI,23 and so on, have been widely investigated by using, for example, rotational-resolved laser absorption,8 laser-induced fluorescence (LIF),9 optical−optical-double-resonance (OODR),3 and stimulated emission pumping (SEP)10 techniques, as well as ab initio calculations.24−29 The structure, spectroscopy, and interactions of the ground state and the lowest singlet/triplet excited states of the halocarbenes have © 2012 American Chemical Society
been studied comprehensively. Although sparse studies concerning higher excited states have emerged, for example, photodissociation dynamics of CHF and CDF at the B state,3−5 CCl2 at 248 nm14,16 and 193 nm,15 and CHCl,6 CFCl, and CFBr at 193 nm.19 Here, we focus on the fluorobromo carbene, CFBr, which has received considerable attention because of its important role in the stratospheric ozone depletion. As all the halocarbenes studied to date, the ground state of CFBr is also a singlet 1A′ state. The singlet−triplet gap (X1A′−a3A″) of CFBr is the largest in all bromocarbenes CXBr (X = H, F, Cl, Br, I), predicated by ab initio calculations, which is attributed to the electronegativity of the substituent as well as the degree of back-donation into the unfilled p-orbital.29 Most studies of CFBr concerned the first excited singlet state A1A″. Although the spectroscopic observation of the A1A″ state has dated back to Merer and Travis’s study in 1966,30 followed by several experimental studies,31−33 the first detailed spectroscopy and photochemistry study was reported in a pair of papers by Kable and co-workers.20,21 Therein, by measuring laser-induced excitation/dispersed fluorescence spectrum and photofragment excitation (PHOFEX) spectrum, as well as by comparing with their ab initio calculations, they concluded that the A1A″ state is predissociated with a barrier at about 3360 cm−1 above the Astate origin. The spectroscopic parameters of the X and A Received: August 9, 2012 Revised: September 24, 2012 Published: September 25, 2012 10435
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Table 1. Equilibrium Geometries and Harmonic Vibrational Frequencies of the Ground State X1A′ and the First Excited Singlet State A1A″ of CFBr calculation this work (CASPT2) cc-pVTZ
cc-pVQZ
RC−F (Å) RC−Br (Å) ∠F−C−Br (deg) ω1 (cm−1) ω2 (cm−1) ω3 (cm−1)
1.298 1.957 106.67 637.3 332.1 1180.0
1.296 1.949 106.68 639.0 333.9 1167.5
RC−F (Å) RC−Br (Å) ∠F−C−Br (deg) ω1 (cm−1) ω2 (cm−1) ω3 (cm−1) T00 (cm−1)
1.315 1.872 125.73 526.1 306.8 1214.1 23328e
cc-pV5Z
Ground Singlet State 1.296 1.945 106.66 640.7 335.2 1164.1 First Excited Singlet State 1.313 1.312 1.855 1.850 125.99 126.03 549.4 559.5 312.9 315.9 1211.6 1212.5 23328e 23328e
literature
experiment
1.291a/1.293b/1.287c 1.949a/1.952b/1.898c 107.0a/106.9b/107.2c 773a/635b/641.7c 361a/332b/345.2c 1252a/1155b/1258.0c
671.2c/666d 348.7c/350d 1198c/1166d
1.306a/1.308c 1.900a/1.842c 125.3a/126.5c 579a/553.1c 301a/327.9c 1267a/1270.2c 23437a
649.5c/494d 336.9c/304d 1134c 20906c/23271.0d
a
Reference 29. bReference24. cReference 20. dReference 22. eCalculated at the CASPT2/cc-pV5Z level, including the scalar relativistic effect and CV correlations; see text for detail.
states, the A state fluorescence lifetimes, and the internal energy of the CF fragment were also determined. Following these studies, recently Truscott et al. reanalyzed the A1A″−X1A′ transition and indicated the origin of the A state should be shifted to 23 271 cm−1 (2365 cm−1 larger than the previous result) by analyzing their dispersed fluorescence spectra and the pattern of 79Br/81Br isotope splitting.22 Several calculations have been carried out regarding the geometries, spectroscopic parameters, and energies of the X, a, and A states.24,26,29 For the states beyond the A state of CFBr, the only study was the 193 nm dissociation experiment reported by Shin and Dagdigian,19 in which they predicated the dissociation of a linear intermediate state according to their observation of the absence of preferential CF Λ-doublet populations. However, the state involved and dynamics of photodissociation are still unknown. In the present work, we reported the results of high level ab initio calculations on CFBr. We carried out CASPT2 calculations on the X1A′ and A1A″ states, and we investigated the dependence of geometric parameters and harmonic frequencies on the selection of basis set. The potential-energy surface (PES) of the A1A″ state along C−Br bond distance was carefully examined at CASPT2/cc-pV5Z level, where the other two geometric parameters were optimized at every C−Br bond length. On this basis, we calculated the barrier height of the A1A″ state using CASPT2 and MRCI+Q methods with different basis sets, including the scalar relativistic effect, spin−orbit coupling (SOC) effect, and core−valence (CV) correlation. Finally, the electronic states of CFBr with energy up to 7 eV were studied. The calculation presented here will provide more comprehensive results about the structure and behavior of electronic states of CFBr radical.
Davidson correction38 (+Q) to account for higher order excitation configurations. The active space consists with 18 valence electrons and 12 valence orbitals corresponding to n = 2 atomic orbitals of C and F atoms and n = 4 orbital of Br atom. The correlation consistent basis sets cc-pVXZ (X = T, Q, 5)39,40 were used in ab initio calculations. The relaxed PES of the A1A″ state along C−Br bond was carefully calculated. We optimized other geometrical parameters of CFBr at every C−Br distance at CASPT2/cc-pV5Z level. The barrier height for A1A″ state was calculated at CASPT2/ccpVXZ and icMRCI+Q/cc-pVXZ (X = T, Q, 5) level with scalar relativistic correction and extrapolated to complete basis set (CBS) limit. We use X−3 extrapolation scheme with formula ΔECORR(X) = ΔECORR(CBS) + acX−3,41 ΔECORR is the dynamical correlation energy calculated with icMRCISD+Q method and ac is a parameter. X = Q, 5 data are used to determine the extrapolated ΔECORR(CBS) value. The scalar relativistic corrections, mass-velocity plus Darwin terms, were obtained with third-order Douglas−Kroll (DK3) approximation42−45 with cc-pVXZ-DK (X = T, Q, 5)39,40 basis sets. The SOC46 corrections are evaluated with state-interacting methods at icMRCI+Q/cc-pVTZ level. Four Λ-S states, lowest singlet A′/A″ and triplet A′/A″ were included in SOC calculations. The core and core−valence electrons correlations of the n = 3 shell for Br were estimated with MRCI+Q methods. The MRCI+Q calculations with inclusion and exclusion of the correlations of the n = 3 shell of Br were performed separately, and then the difference between the two energies yields CV correlation. The cc-pwCVTZ basis sets47,48 for Br, F, and C were used for both frozen-core and CV calculations. The one-dimensional potential energy cuts of 12 electronic states of CFBr computed at CASPT2/cc-pVTZ level were given with respect to the angle of F−C−Br, C−Br distance, and C−F distance, respectively, with the other two parameters fixed at their respective equilibrium values. The oscillator strengths for different excited states to ground state are calculated at CASSCF/cc-pV5Z level. All calculations were carried out using the MOLPRO software package.49
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METHODS In our work the ground and first excited singlet states, X1A′ and A1A″ were investigated using complete active space secondorder perturbation (CASPT2) theory34,35 and internally contracted singly and doubly excitation multireference configuration interaction (icMRCISD) method 36,37 with 10436
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Figure 1. (a) Potential-energy surfaces of the A1A″ state along the C−Br bond coordinate calculated at CASPT2/cc-pV5Z level. (b) Dependence of the C−F bond length and F−C−Br angle on the C−Br bond length at CASPT2/cc-pV5Z level.
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A1A″ state are in good agreement with the previous CASPT2 results20 and recent MRCI results29 within 0.006 Å for C−F bond length, 0.05 Å for C−Br bond length, and 0.7° for F−C− Br angle. Our calculated ω1 value is well consistent with other calculation results but is about 90 cm−1 smaller than experimental result of ref 20 and about 65 cm−1 larger than experimental result of ref 22. The present value of bending frequency is as much as 15 and 21 cm−1 difference from the others’ calculations and experimental results. Our calculated frequency of ω3 is about 50 cm−1 underestimated in comparison with previous theoretical results, but more close to the experimental value. The A1A″ state transition energy with inclusion of zero-point energy was 22 294 cm−1 calculated at CASPT2/cc-pV5Z level. Including the scalar relativistic effect (CASPT2/cc-pVTZ+DK) and CV correlations of n = 3 shell (CASPT2/cc-pwCVTZ), additional corrections of 878 and 156 cm−1 were observed, resulting a calculated T00 value of 23 328 cm−1. Our result of T00 was in good agreement with recent MRCI calculations29 (23 328 vs 23 437 cm−1) and only 57 cm−1 higher than the latest experimental result22 (23 328 vs 23 271 cm−1). B. Barrier Height of the A1A″ State. It is well realized that the A1A″ state of the CFBr radical is a predissociation state. However, there is still a discrepancy in the barrier height along the dissociation pathway of CF + Br channel. In experiment, Kable and co-workers21 measured both LIF and PHOFEX spectra of the A1A″ state and conclude a barrier height of 3360 ± 50 cm−1. Recently, Truscott et al. reanalyzed the A1A″−X1A′ transition of CFBr, using LIF spectroscopy at sub-Doppler resolution.22 With reassignment of T00 of the A1A″ state to 23 271 cm−1 (2365 cm−1 higher than Kable’s result), they deduced that the barrier height should be less than 1000 cm−1 because only four lowest vibrational states (up to (020)) of the A1A″ state have significant quantum yields for fluorescence. Theoretically, Kable and co-workers20 calculated a barrier height of 3455 cm−1 above the zero- point of the A1A″ state at the CASPT2/cc-pVTZ level, consistent with their experimental results. Later, Standard and Quandt23 reported different values of the barrier, 953, 2150, and 2776 cm−1, calculated using the CASPT2 method with different basis sets SBKJC(3d), SBKJC(3df), and Basis3(SBKJG(3df) for Br plus DZ(3df) for C and F), respectively. To shed more light on the character of the A1A″ state of CFBr radical, we first carefully examined the PES of the state along the C−Br bond distance at CASPT2/cc-pV5Z level, as shown in Figure 1a. Unlike general PES calculation that fixes
RESULT AND DISCUSSION A. Equilibrium Geometries and Harmonic Vibrational Frequencies of the Ground State and the First Excited Singlet State. The equilibrium bond lengths, bond angles, and harmonic vibrational frequencies and energies of the ground state (X1A′) and the first excited singlet state (A1A″) of CFBr are listed in Table 1, calculated using the CASPT2 method with three different basis sets, cc-pVTZ, cc-pVQZ, and cc-pV5Z. There are little pronounced changes in the calculated geometries of both X1A′ and A1A″ states as the basis set is increased from cc-pVTZ to cc-pV5Z, in accordance with the previous MRCI calculation of CHBr radical.29 The three harmonic vibrational frequencies of the X1A′ state change as much as 16 cm−1 from the cc-pVTZ to cc-pV5Z level. The largest change observed in our calculation as the results of the basis sets is the low-frequency stretch mode ω1 of the A1A″ state, of which the frequency increases 33.4 cm−1 from ccpVTZ to cc-pV5Z level. In addition, our results show deviation between cc-pVQZ and cc-pV5Z level is less than that between cc-pVTZ and cc-pVQZ level, indicating that the accuracy is systemically improved by using larger basis set. For comparison, we also listed in the table the calculated and experimental results reported in the literature. For the X1A′ state, our geometry results show good agreement with the previous calculations: only 0.005 Å (bond lengths) and 0.3° (F−C−Br angle) different from the most recent MRCI calculation.29 The harmonic vibrational frequency of the bending mode ω2 is also in reasonable agreement with the previous computational results,20,24,29 and within 15 cm−1 difference from experimental results.22 The largest difference among the calculation is observed in the frequencies of the stretching modes. For low-frequency stretching mode ω1, the MRCI result29 is as much as ∼130 cm−1 larger than our result and previous CASPT220 and QCISD24 results; for highfrequency stretching mode ω3, our result is close to QCISD result24 but is about 100 cm−1 smaller than other previous calculation results.20,29 In contrast, the present calculation results are in much better agreement with the most recent experimental results:22 within 25 cm−1 for ω1 and less than 2 cm−1 for ω3. For the A1A″ state, both the C−F bond distance and the F− C−Br angle increase, whereas the C−Br bond distance decreases comparing to those of the ground state, due to the transition of 19a′−7a″, which corresponds to excitation of nonbonding electron of carbon atom to empty out-plane p orbital of carbon. The present equilibrium geometries of the 10437
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the other geometric parameters at the equilibrium point as the C−Br bond length is changing, we optimized the geometric parameters at each step of the calculation. Indeed, our results show that the C−F bond length and the F−C−Br angle change as the C−Br bond length varies (Figure 1b). Only one maximum point but no other saddle point is found on the PES of the A1A″ state, which confirms the presence of the dissociation barrier along the C−Br bond. The geometric parameters of the saddle point are 1.285 Å (C−F bond length), 2.347 Å (C−Br bond length), and 119.50° (F−C−Br angle), and the harmonic frequencies are 200.8 cm−1 (ω1), 237.6i cm−1 (ω2), and 1245.0 cm−1 (ω3). With the above optimization of the structure along the C−Br bond distance, we calculated the barrier height with the CASPT2 and MRCI+Q methods. We investigated the dependence of the calculated value on the basis set, and we also included the scalar relativistic effect, SOC effect, and CV correlation in the calculation. The results are shown in Table 2.
Figure 2. Potential energy curves of CFBr with respect to the F−C− Br angle calculated at the CASPT2/cc-pVTZ level. The C−F and C− Br bond lengths were fixed at their respective equilibrium values.
Table 2. Barrier Height of the A1A″ of CFBr Calculated with Different Methods and Basis Sets (cm−1) cc-pVTZ cc-pVQZ cc-pV5Z CBS +CV +SOC total
CASPT2
CASPT2+DK
MRCI+Q
MRCI+Q+DK
1329 1829 2040 2106 347 −22 2431
756 1404 1641 1863 347 −22 2188
651 1307 1546 1770 347 −22 2095
435 1083 1320 1542 347 −22 1867
Unlike the geometric parameters and harmonic vibrational frequencies shown in Table 1, which has less pronounced dependence on the basis set, the barrier height of the A1A″ state changes significantly with different basis sets. Particularly, the value calculated with any method at the cc-pVTZ level is apparently underestimated. With CV and SOC corrections, the barrier height calculated at MRCI+Q+DK/CBS levels is 1867 cm−1. This barrier height is 1493 cm−1 lower than the previous experimental result reported in ref 21 (1867 vs 3360 cm−1), possibly due to the under-evaluated T00 value of the A1A″ state in their study (also see different T00 values in Table 1). Our result is about 867 cm−1 higher than the estimated barrier height in the recent experimental study,22 which can be understood because the barrier height deduced from fluorescence quantum yield could be underestimated. C. High Electronic Excited States of the CFBr Radical. In the present study, we investigated a total of 12 electronic states of the CFBr radical with vertical transition energy (VTE) up to 7 eV. In the above sections, we have presented in detail our calculation results of the ground state X1A′ and the first excited A1A″ state. In this section, we will turn to discuss the other higher electronic excited states. To the best of our knowledge, to date there are no theoretical studies concerning the electronic states above the A1A″ state, and the only experimental result is photodissociation dynamics study at 193 nm carried out by Shin and Dagdigian.19 Figures 2−4 show the rigid one-dimensional potential energy cuts along the F−C−Br angle, C−F bond, and C−Br bond, respectively, calculated at the CASPT2/cc-pVTZ level. In each figure, the other two geometric parameters were fixed at their respective equilibrium values. Table 3 lists our results of the VTE, the electron
Figure 3. Potential energy curves of CFBr with respect to the C−F bond calculated at the CASPT2/cc-pVTZ level. The C−Br bond length and the F−C−Br angle were fixed at their respective equilibrium values.
configuration, the oscillator strength, and the transition of each electronic state of the CFBr radical. Similar with the X1A′ (11A′) and A1A″ (11A″) state, the first triplet state a3A″ (13A″) state is also bent with an energy minimum at a F−C−Br angle of ∼120° (Figure 2). The singlet−triplet gap is about 11 179 cm−1, which is consistent with previous calculations.29 For other excited states, 31A″, 23A′, 33A′, and 33A″ are bending states, whereas 13A′, 23A″, 21A″, 21A′, and 31A′ are considered to be linear (or quasilinear) states with the global energy minimum at ∼180°. Avoided crossing points between different states may be found in bending potentials, cf. 13A′−23A′ states at F−C−Br angles of 70° and 120°, 11A″−21A″ states at 90° (Figure 2), indicating strong coupling exists in these conical intersection regions. For most of the calculated electronic states, the C−F bond is bound (Figure 3). Dissociation barriers are observed in some states along the C−F bond, which may be attributed to the coupling between states with the same symmetry. For example, the coupling in avoided crossing point between 13A′ and 33A′ states leads to the dissociation barrier in the 13A′ state. In 10438
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CHF5 where a repulsive singlet state intersecting with the B1A′ state was implied. The 31A′ state with a VTE of 6.39 eV may be assigned as the state excited in the 193 nm photodissociation (photon energy of 6.42 eV) in ref 19. The state is a linear state (Figure 2), supporting the predication made in ref 19. A very small difference of VTE between the triplet states (33A′ and 33A″) and the 31A′ state indicates that strong state interaction is unavoidable and the triplet states should be involved in the 193 nm photodissociation. Future work will no doubt be necessary to carry out to reveal the complicated dynamics of high excited states of CFBr radical.
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CONCLUSION In conclusion, we have carried out a comprehensive theoretical study on the ground and excited states of fluorobromo carbene, CFBr, by employing high-level CASPT2 and MRCI methods. The calculated geometric parameters and harmonic vibrational frequencies of the ground X1A′ state and the first excited singlet A1A″ state, using CASPT2/cc-pVXZ (X = T, Q, 5), were in good agreement with previous experimental and theoretical results and showed no significant dependence on the basis sets. The adiabatic transition energy T00 of the A1A″ state was calculated to be 23 328 cm−1 at the CASPT2/cc-pV5Z level including scalar relativistic and CV corrections, which is only 57 cm−1 higher than the latest experimental result. To elucidate the barrier height of the predissociative A1A″ state, we first examined the PES along the C−Br bond distance at the CASPT2/cc-pV5Z level, by optimizing the C−F bond and F− C−Br angle at every C−Br bond length. From there, we calculated the barrier height of the A1A″ state by CASPT2 and MRCI+Q methods with different basis sets, considering the scalar relativistic effect, SOC effect, and CV correlation. The barrier height calculated at MRCI+Q+DK/CBS levels is 1867 cm−1. Finally, the PESs along three coordinates, the vertical transition energies, the electronic configurations, and the available oscillator strengths of total 12 states of CFBr were calculated. It is indicated that there exist strong interactions
Figure 4. Potential energy curves of CFBr with respect to the C−Br bond calculated at the CASPT2/cc-pVTZ level. The C−F bond length and the F−C−Br angle were fixed at their respective equilibrium values.
contrast to bound or quasi-bound C−F potential energy cuts, all C−Br potential energy cuts are purely repulsive, leading to Br + CF fragments, except for the bound X1A′ and a3A″ states and the predissociative A1A″ state (Figure 4). The dissociation barrier of the A1A″ state discussed in the above section could be arising from the interaction between the A state with these repulsive states, particularly the singlet and triplet states with VTE of 4−5 eV. Above the A1A″ state, the 21A″ and 21A′ states are the next two excited states with apparent oscillator strength. Comparing to the B state of CHF5, which is a 1A′ state, the second excited singlet state of CFBr could be a 21A″ state with a VTE of 4.64 eV. However, the 21A′ state is only 0.46 eV above the 21A″ state but has a 2 orders of magnitude larger oscillator strength. Curve crossing along the C−Br coordinate between these two states of CFBr can be observed (Figure 3), as in the B state of
Table 3. VTE, Oscillator Strength, Electron Configuration, and Transition of Electronic States of CFBr
a
state
VTE (eV)
oscillator strength
11A′ 13A″
0 1.39
11A″
2.87
13A′ 23A″
4.07 4.12
21A″
4.18
8.00 × 10−5
21A′ 23A′
4.64 4.75
0.009 52
33A′
6.25
31A′
6.38
0.031 54
33A″ 31A″
6.39 6.88
0.007 984
0.006 53
main configuration
excitationa
(6a″)2 (18a′)2 (19a′)2 (6a″)2 (18a′)2 (19a′)(7a″) (17a′)2(6a″)2(18 a′)(19 a′)2(7a″) (6a″)2(18a′)2(19a′)(7a″) (17a′)2(6a″)2(18a′)(19a′)2(7a″) (5a″)2(6a″)(18−19a′)2(7a″) (17a′)2(6a″)2(18a′)(19a′)2(7a″) (6a″)2(18 a′)2(19a′)(7a″) (17a′)2(6a″)2(18a′)(19a′)2(7a″) (6a″)2(18a′)2(19a′)(7a″) (5a″)2(17a′)2(6a″)(18a′−19a′)2(7a″) (6a″)2(18a′)2(19a′)(20a′) (17 a′)2(6a″)2(18a′)(19a′)2(20a′) (17a′)2(6a″)2(18a′)(19a′)2(20a′) (6a″)2(18a′)2(19a′)(20a′) (6a″)2(18a′)2(19a′)(20a′) (17a′)2(6a″)2(18a′)(19a′)2(20a′) (5a″)2(17a′)2(6a″)(18−19a′)2(20a′) (5a″)2(6a″)(18−19a′)2(20a′)
19a′ → 7a″(0.506) 18a′ → 7a″(0.384) 19a′ → 7a″(0.586) 18a′ → 7a″(0.319) 6a″ → 7a″(0.918) 18a′ → 7a″(0.515) 19a′ → 7a″(0.417) 18a′ → 7a″(0.594) 19a′ → 7a″(0.340) 6a″ → 7a″(0.774) 19a′ → 20a′(0.577) 18a′ → 20a′(0.273) 18a′ → 20a′(0.596) 19a′ → 20a′(0.327) 19a′ → 20a′(0.702) 18a′ → 20a′(0.155) 6a″ → 20a′(0.791) 6a″ → 20a′ (0.908)
The value in parentheses refers to the coefficient of the corresponding configuration. 10439
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(28) Sendt, K.; Schmidt, T. W.; Bacskay, B. G. Int. J. Quantum Chem. 2000, 76, 297−305. (29) Standard, J. M.; Steidl, R. J.; Beecher, M. C.; Quandt, R. W. J. Phys. Chem. A 2011, 115, 1243−1249. (30) Merer, A. J.; Travis, D. N. Can. J. Phys. 1966, 44, 1541−1550. (31) Prochaska, F. T. J. Chem. Phys. 1980, 73, 2651−2664. (32) Miller, J. C.; Andrews, L. J. Phys. Chem. 1980, 84, 401−403. (33) Schlachta, R.; Lask, G.; Bondybey, V. E. Chem. Phys. Lett. 1991, 180, 275−278. (34) Werner, H.-J. Mol. Phys. 1996, 89, 645−661. (35) Celani, P.; Werner, H.-J. J. Chem. Phys. 2000, 112, 5546−5557. (36) Werner, H.-J.; Knowles, P. J. J. Chem. Phys. 1988, 89, 5803− 5814. (37) Knowles, P. J.; Werner, H.-J. Chem. Phys. Lett. 1988, 145, 514− 522. (38) Langhoff, S. R.; Davidson, E. R. Int. J. Quantum Chem. 1974, 8, 61−72. (39) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007−1023. (40) Wilson, A. K.; Woon, D. E.; Peterson, K. A.; Dunning, T. H., Jr. J. Chem. Phys. 1999, 110, 7667−7676. (41) Helgaker, T.; Klopper, W.; Koch, H.; Noga, J. J. Chem. Phys. 1997, 106, 9639−9646. (42) Reiher, M.; Wolf, A. J. Chem. Phys. 2004, 121, 2037−2047. (43) Reiher, M.; Wolf, A. J. Chem. Phys. 2004, 121, 10945−10956. (44) Wolf, A.; Reiher, M.; Hess, B. A. J. Chem. Phys. 2002, 117, 9215−9226. (45) de Jong, W. A.; Harrison, R. J.; Dixon, D. A. J. Chem. Phys. 2001, 114, 48−53. (46) Berning, A.; Schweizer, M.; Werner, H.-J.; Knowles, P. J.; Palmieri, P. Mol. Phys. 2000, 98, 1823−1833. (47) DeYonker, N. J.; Peterson, K. A.; Wilson, A. K. J. Phys. Chem. A 2007, 111, 11383−11393. (48) Peterson, K. A.; Dunning, T. H. J. Chem. Phys. 2002, 117, 10548−10560. (49) Werner, H.-J.; Knowles, P. J.; Lindh, R.; Manby, F. R.; Sch€utz, M.; Celani, P.; Korona, T.; Mitrushenkov, A.; Rauhut, G.; Adler, T. B.; et al. MOLPRO, a package of ab initio programs, 2009.
between different states, leading to complicated dynamics of the electronic states, especially high excited states of CFBr.
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AUTHOR INFORMATION
Corresponding Author
*H.X.: tel, 86-431-85168817; fax, 86-431-85168816; e-mail,
[email protected] B.Y.: e-mail,
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by National Basic Research Program of China (973 Program) (2013CB922200) and National Magnetic Confinement Fusion Science Program of China (2010GB104003). H.X. acknowledges the financial support by National Natural Science Foundation of China (11034003, 11074095 and 11274140).
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