Structure and Stability of C20H3 Radical

Chinese Journal of Chemistry, 2008, 26, 2307—2316 Full Paper

* E-mail: [email protected]; Tel.: 0086-757-83106905 Received August 20, 2007; revised April 23, 2008; accepted August 12, 2008. Project supported by the National Natural Science Foundation of China (No. 20471034) and Youth Foundation of Shanxi (No. 20051011).

© 2008 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Structure and Stability of C20H3 Radical

REN, Jie*,a(任洁) ZHANG, Cong-Jieb(张聪杰) WU, Hai-Shunb(武海顺) a Deparment of Light Industry and Chemistry, Guangdong Institute of Textile Technology, Foshan,

Guangdong 528041, China b Department of Chemistry, Shanxi Normal University, Linfen, Shanxi 041004, China

Density functional theory B3LYP with 6-31G* basis set has been used to investigate the geometries, rotational constants, dipole moments, energy gaps and vibrational frequencies of nine series of isomers of C20H3 radical. The result shows that the bowl-like structure with C1 symmetry is the most stable structure, in which the three hydrogen atoms locate on the edge carbon atoms, and the two hydrogen atoms are neighbouring and the other one has a two- carbon atom interval to the neighbouring hydrogen. In addition, the relationship between the energy and the position of one hydrogen atom from end to middle on the linear structures of C20H3 radical with two hydrogens atoms lo-cated on two ends was obtained, which shows the energy increase monotonously. Furthermore, hydrogenation can relax the strain and make the isomer of C20 more stable.

Keywords C20H3 radical, structure and stability, density functional theory

Introduction

Identity of the carriers of the diffuse interstellar bands (DIB) is an unsolved problem in chemistry, physics and astronomy fields. In general, the highly un-saturated hydrocarbons and pure carbon clusters are considered as candidate carriers of DIB, because their size and structure are consistent with absorption of visi-ble radiation.1,2 Molecules of the generic formula CnHm (m≤n) are abundant in flames and plasmas involving hydrocarbon precursors. These species are therefore of paramount importance in the formation of polycyclic aromatic hydrocarbons and subsequent soot formation.3 Again, such molecules are effectively detected by the experimental methods, such as the matrix isolation spectroscopy, Fourier transform microwave spectros-copy (FTM), cavity ringdown spectroscopy (CRDS), resonance enhanced two-color photo detachment spec-troscopy and resonance two-color two-photon ionization (R2C2PI) and so on.4-6

Of the molecules with formula CnH, only one type of isomer has been observed in the laboratory: that with the hydrogen atom terminating one end of the carbon chain. Moreover, CnH (n＝1—8) have been confirmed to exist in space.3,7,8 The structures and electron transi-tion energies of C2nH were also investigated by ab initio method and density functional theory.9 The even poly-yne chains, HC2nH, have been observed in rare gas ma-trices by direct absorption spectroscopy and in the gas phase by 1＋1' resonance enhanced multi-photon ioni-zation spectroscopy (REMPI).6,10 The odd polyyne radical chains, HC2n＋1H (n＝3—6), were also detected in matrices by direct absorption and in the gas phase by

cavity ringdown spectroscopy.5 And the linear and nonlinear behavior of wavelength of the original band of the electron transition of CnH2 vs. the number of carbon atoms was investigated for odd- and even-number n in experiment and theory.11 The wide variety of CnH2 iso-mers measured by microwave spectroscopy leads one to assume that more isomers may be observed for the cor-responding CnH3 series, as illustrated by Mebel et al.12 The identity of the structures of the CnH3 radicals is very important in interstellar, combustion and plasma chemistry. Specially, the species are of paramount im-portance in the formation of polycyclic aromatic hydro-carbons and subsequent soot formation.13,14 Recently, CnH3 (n＝7—29) radicals were observed in experi-ment.13-15 As for the small molecules, the structures, microwave spectroscopy and infrared laser spectroscopy of C3H3 were investigated in theory and experiment.16 The stable structures of C5H3 radical were obtained us-ing an ab initio method.12 The C7H3 radical has been recently observed by 1＋1' REMPI and the structure and rotational constants were obtained at the DFT level employing a B3LYP functional, confirming that a three-membered ring isomer is the carrier of the ob-served spectra in the gas phase.17 Subsequently, Maier and co-workers recorded the resonant two-color two-photon spectra of C9H3, C11H3 and C13H3 in the gas phase and found that there was a remarkably similar vibrational structure among the three radicals.13 The structure, stability and spectra of C9H3, C11H3 and C13H3

were investigated by DFT and TD-DFT18 and isomers HC4(HC)C4H, HC4(C(C2H))C4H and C(C4H)3 were considered as the possible carriers of the spectra on ex-

2308 Chin. J. Chem., 2008, Vol. 26, No. 12 REN, ZHANG & WU


periment.13 It is known that the smallest carbon fullerene is C20.

Its structure and stability have been widely studied in theory.19 The results of experiment show that C20H3 radical exists in gas phase. However, information about its structure is less known to us in both experiment and theory. In this paper, we will detailedly investigate the structures, the stability, rotational constants, dipole moments, energy gaps and vibrational frequencies of C20H3 radical in theory.

Computational method

In general, three types of C20 isomers of single ring, bowl-like and fullerene are considered to be more sta-ble.19 In addition, the previous results indicate that the stable structures of CnHm radicals have dominant single triple bond alternation of carbon chain. Thus, we class the isomers of C20H3 radical into nine series of possible structures, i.e. open chain, twenty-membered, eight-een-membered, sixteen-membered, fourteen-membered, twelve-membered and ten-membered rings, bowl-like and fullerene. The possible structures of each group were optimized by B3LYP functional with 6-31G* basis set. And, the vibrational frequencies, rotational con-

stants, dipole moments, energy gaps were calculated at the same level. All calculations were carried out with the Gaussian 98 program.20

Results and discussion

Structure and stability of C20H3 radical

Within each group, the structures differ by the dis-tribution of three hydrogen atoms. For example, there are ten types of isomers in the chain group, in which a hydrogen atom moves from end to the tenth carbon atom of linear HC20H. Because there are plenty of iso-mers in each group, the symmetry, electron state, total energies, relative energies, rotational constants A, B and C and dipole moments of the first four more stable structures of each group of C20H3 radical are listed in Table 1. And the geometries of these isomers are dis-played in Figures 1 to 9. As can be seen from Figure 1, one hydrogen atom partitions the long chain structure of HC20H into two parts, then, the number of carbon atoms of one part is even while the other part is odd. Moreover, the linear chain parts in each isomer have single and triple bond alternation and show a polyacetylenic struc-ture in the even part, and the C—C bonds near the mid-

Figure 1 The first four stable isomers for the open chain (bond length in Å).

C20H3 radical Chin. J. Chem., 2008 Vol. 26 No. 12 2309


Table 1 Symmetry, electron state, total energies, relative energies, rotational constants and dipole moments of the first four stable structures of each series of C20H3 radicals

Isomer Sym. State E/a.u. RE/eV A/cm－1 B/cm－1 C/cm－1 D/Debye

A1 C2v 2B2 －763.37000 0.00 9.71548 0.00123 0.00123 1.1208

A2 Cs 2A' －763.35439 0.42 0.29452 0.00127 0.00127 0.2041

A3 Cs 2A' －763.35211 0.49 0.06879 0.00136 0.00134 0.4794

A4 Cs 2A' －763.35069 0.53 0.03565 0.00145 0.00140 0.8548

B1 Cs 2A' －763.38772 0.00 0.01633 0.00561 0.00418 1.7959

B2 Cs 2A' －763.38313 0.12 0.01250 0.00633 0.00420 1.9945

B3 Cs 2A' －763.37491 0.35 0.00982 0.00726 0.00418 2.6364

B4 Cs 2A' －763.37185 0.43 0.01234 0.00625 0.00415 1.4538

C1 Cs 2A' －763.37726 0.000 0.01782 0.00555 0.00423 2.0660

C2 Cs 2A' －763.37714 0.003 0.01953 0.00537 0.00421 1.3793

C3 Cs 2A' －763.37713 0.004 0.01710 0.00575 0.0043 1.5361

C4 Cs 2A' －763.37674 0.014 0.02133 0.00521 0.00419 1.4434

D1 Cs 2A' －763.35553 0.000 0.02892 0.00421 0.00368 2.0249

D2 Cs 2A' －763.35476 0.021 0.02507 0.00449 0.00381 1.3488

D3 Cs 2A' －763.35453 0.027 0.02793 0.00434 0.00376 1.1465

D4 Cs 2A' －763.34721 0.226 0.01636 0.00527 0.00399 2.1994

E1 Cs 2A' －763.36583 0.000 0.02823 0.00363 0.00321 2.1646

E2 Cs 2A' －763.36549 0.009 0.03594 0.00347 0.00316 1.1317

E3 Cs 2A' －763.36540 0.011 0.02536 0.00386 0.00335 1.1631

E4 Cs 2A' －763.36496 0.024 0.04020 0.00332 0.00307 2.2853

F1 Cs 2A' －763.33608 0.000 0.05394 0.00263 0.00251 2.034

F2 Cs 2A' －763.33483 0.034 0.04394 0.00277 0.00260 0.9641

F3 Cs 2A' －763.33471 0.037 0.05218 0.00269 0.00256 0.7292

F4 C2v 2B2 －763.32344 0.344 0.03021 0.00305 0.00277 0.4918

G1 Cs 2A' －763.35082 0.000 0.07724 0.00215 0.00209 1.2744

G2 Cs 2A' －763.35074 0.002 0.05912 0.00221 0.00213 1.9519

G3 Cs 2A' －763.35034 0.013 0.05593 0.00227 0.00218 0.6954

G4 Cs 2A' －763.35015 0.018 0.08543 0.00213 0.00208 0.6906

H1 C1 2A －763.46855 0.00 0.01856 0.01811 0.00943 2.6806

H2 C1 2A －763.46811 0.01 0.01885 0.01785 0.00942 3.1453

H3 C1 2A －763.46770 0.023 0.01917 0.01754 0.00942 1.1695

H4 C1 2A －763.46765 0.024 0.01894 0.01774 0.00942 1.8428

I1 Cs 2A' －763.38144 0.00 0.02580 0.02368 0.02297 3.1585

I2 C1 2A －763.37812 0.09 0.02626 0.02326 0.02277 1.2103

I3 Cs 2A' －763.37677 0.13 0.02527 0.02396 0.02320 2.7362

I4 C1 2A －763.37610 0.15 0.02527 0.02396 0.02320 2.1044

dle hydrogen atom are cumulenic bonding. For example, in isomer A3, there are four carbon atoms in the left of the middle hydrogen atom, and the bond distance from the left to right is 1.215, 1.360, 1.244 and 1.408 Å, re-spectively. And there are fifteen carbon atoms in the right of the middle hydrogen atom, and the bond dis-tance from the left to right is sequentially 1.342, 1.271, 1.287, 1.288, 1.272, 1.302, 1.261, 1.314, 1.251, 1.324, 1.243, 1.334, 1.234, 1.352 and 1.218 Å, respectively. The distance of C—H bonds is about 1.067 Å for the carbon atom with sp hybrid and about 1.090 Å for the

carbon atom with sp2 hybrid. The four isomers shown in Figure 1 are more stable than other open chain isomers according to the calculated results in this work. As can be seen from Figure 1, their structures are similar, in which the number of carbon atoms in the even part is less than that in the odd one. In order to explore the re-lationship between the energies and the position of the middle hydrogen atom, the curve of the relative energy of the possible isomers vs. the position of hydrogen atom in the linear chain of HC20H was obtained and shown in Figure 10. As can be seen from Figure 10, the



Figure 2 The first four stable isomers for the twenty-membered ring (bond length in Å).

Figure 3 The first four stable isomers for the eighteen-membered ring (bond length in Å).

energies increase as the number of carbon atoms in the even part of linear HC20H increases. Then the most sta-ble linear structure is isomer A1 and the energy of the next stable structure A2 is 0.42 eV higher than that of isomer A1. Isomer A1 has a similar structure as C9H3, C11H3 and C13H3, whose two hydrogen atoms locate on one end and the other on the other end and has C2v sym-metry.18

From Table 1, the most stable isomers of the six groups of ring structures from the twenty- to

ten-membered ring are isomers B1, C1, D1, E1, F1 and G1, respectively. Within each group, the first four iso-mers differ by the distribution of three hydrogen atoms, and the energy difference is very small, indicating that position of hydrogen atoms has little influence on the single ring structures. Furthermore, we can find that a group of characteristic numbers are 8, 6, 6, 4, 4 and 2, respectively, which are the number of conjoint even carbon atoms in rings of the isomers B1, C1, D1, E1, F1 and G1.



Figure 4 The first four stable isomers for the sixteen-membered ring (bond length in Å).

Except for the twenty-membered ring, there is a —CnH radical in the other single ring isomer. In the single ring isomers, the bond length of C—H is about 1.09 Å in which the H atom locates on the ring. And the bond distance of C—H is close to 1.067 Å in which the H atom locates at the end of the linear chain part.

There are ten types of isomers of bowl-like with different positions of hydrogen atoms. And the more stable structures are H1, H2, H3 and H4 shown in Figure 8, which are all the possible isomers in which the two hydrogen atoms keep adjoining.

The last series is cage-like. When we add three H atoms in the cage, thirteen different structures will be obtained, in which the energies of four structures, I1, I2,

Figure 5 The first four stable isomers for the fourteen-membered ring (bond length in Å).

I3 and I4 are less than those of others. And, the symmetry, electron state, total energies, relative energies, rota-tional constants A, B and C and dipole moments of the four structures are listed in Table 1. The most stable structure of fullerene of C20H3 is I1, in which the three hydrogen atoms locate on a five-membered ring and they are conjoint. The structure takes a Cs symmetry and the bond lengths of C—H are 1.093 Å.

As can be seen from Table 2, the order of energies of the most stable structure in each group is bowl-like＜twenty-membered ring＜cage-like＜eighteen-membered ring＜open chain＜fourteen-membered ring＜sixteen-membered ring＜ten-membered ring＜twelve- membered ring. B1 lies 2.20 eV higher in relative en-ergy than H1. The difference value is big. Thereby the bowl-like is especially stable. Its stability was attributed to that twenty carbon atoms form a larger delocalized conjugated-π bond. Its energy is －763.46855 hartree,



Figure 6 The first four stable isomers for the twelve-membered ring (bond length in Å).

Table 2 Symmetry, total energies, relative energies and energy gaps of the most stable isomers in each group

Isomer Sym. E/a.u. RE/eV ∆Eg/a.u.

A1 C2v －763.37000 2.68 0.07144

B1 Cs －763.38772 2.20 0.06832

C1 Cs －763.37726 2.48 0.08856

D1 Cs －763.35553 3.08 0.06852

E1 Cs －763.36583 2.80 0.10148

F1 Cs －763.33608 3.60 0.07162

G1 Cs －763.35082 3.20 0.11385

H1 C1 －763.46855 0.00 0.13989

I1 Cs －763.38144 2.37 0.09378

while that of bowl-like C20 is －761.49159 hartree.

Figure 7 The first four stable isomers for the ten-membered ring (bond length in Å).

Though the energy decreases after C20 with three H at-oms, the relative energy is small. Because the electro-negativity of H atom is small, its influence is little on stability. As clarified by Figure 12, the energy curve is like sawtooth as the single ring becomes larger from eighteen-membered ring to ten-membered ring.

It is a big series from twenty-membered ring to ten-membered ring. The most stable isomer of each group all has neighbouring substituent, which is away from another substituent with even-number carbon at-oms that is smaller than ten. In addition, the three sub-stituents in the ring divide the ring into two arcs. The difference value of the number of carbon atoms presents rule between two arcs. The difference value is one and three alternation from B1 to G1. Other isomers, which have two H atoms at the end of carbon chain and one H atom in the ring, are less stable than these isomers. For example, G5 does not have the same single-triple bonds as G1 in the linear chain part. As shown in Figure 11, C(1)—C(2) and C(2)—C(3) in the linear chain part



Figure 8 The first four stable isomers for the bowl-like structure (bond length in Å).

Figure 9 The first four stable isomers for the cage structure (bond length in Å).

Figure 10 Position of the third hydrogen atom on the linear chain of HC20H vs. the relative energy.

are cumulenic bonding. It owns less single-triple bonds than G1. Polyacetylenic structure has large influence on stability. The more the number of single-triple bonds is, the larger the delocaization is, and more stable the iso-mer is.

The most stable structure is the open chain isomer with C2v symmetry for CnH3 (n＝7, 9, 11 and 13).18 But the most stable isomer of C20H3 is the bowl-like with C1

symmetry, which is consistent with the Reference 21. It is different from the series for small n. The stability of the twenty-membered ring is only under the bowl-like. The next is the cage-like. The result can be obtained that it is important to build the isomers of the single ring structure and cage-like structure for larger series of CnH3 radicals.



Figure 11 An unstable isomer of the ten-membered ring (bond length in Å).

Figure 12 Relative energies of thirty-six stable isomers.

Rotational constants, dipole moments and energy gaps

The rotational constants play an important role in as-signing the isomer carried spectra.

The rotational constant A of A1—A4 decrease as the energy increases. The dipole moments are all remarka-bly less than those of the other structures. The largest is only 1.176 Debye. For the twenty-membered ring the rotational constant A of B1 is the biggest. B3 has the largest dipole moment. The rotational constant A of curve eighteen-membered ring is sawtooth-like. C1 has the largest dipole moment. D1 is the most stable struc-ture in the sixteen-membered ring, while its rotational constant A is the largest. The rotational constant A curve of D1—D4 is also like sawtooth. D4 has the largest di-pole moment. The same as above, the four-teen-membered ring and twelve-membered ring rota-tional constant A curve are like sawtooth, too. The di-pole moments of E4 and F1 are the largest in their group, respectively. We confirmed that the 18-, 16-, 14- and 12-membered ring isomers had the same order for the rotational constant A: its curve is like sawtooth as the stability decreases in each group. The configuration of G4 has the largest rotational constant A for the ten-membered ring. G1 that is the most stable configu-ration in the ten-membered ring has the largest dipole moment. The rotational constants B and C of all isomers of C20H3 radical have a little difference. The rotational constants of the bowl-like are similar to those of the cage-like. The rotational constants A, B and C have a little difference. H2 and I1 have the largest dipole mo-ment in the groups of H and I, respectively.

Figure 13 shows the energy gap of the most stable configuration in each group. The figure is like sawtooth from A1 to G1. The trend is decreasing as energy from A1 to B1. From C1 to I1, the crest of energy gap chart is the trough of relative energy chart. And the isomer of the lowest energy (H1) has the largest energy gap.

Figure 13 Energy gap of the most stable isomer in each group.

Vibrational frequencies of C20H3

The vibrational frequencies of the isomers of C20H3 were calculated using B3LYP functional with 6-31G* basis set. In order to confirm the characters of the iso-mers and the bonds, the lowest vibrational frequencies, the stretching vibration model of C≡C bond and strongest IR vibrational model are displayed in Table 3.

In Table 3, four isomers of open chain have the low-est frequency near 10 cm－1. The vibrational model of A1 is the bending of the long carbon chain. The vibra-tional way of the lowest frequency of isomers A2, A3 and A4 is the bending of the two carbon chains. For the twenty-membered ring, the four isomers also have the lowest frequency near 40 cm－1. Though there is not a linear carbon chain, the polyacetylenic structure exists in the carbon ring. So the lowest frequency can be ob-tained. It is the bending of the whole ring. The vibra-tional frequencies have large difference between the open chain and twenty-membered ring. The frequency near 2100 cm－1 is the stretching of C≡C bond for all the isomers, which confirms that the single and triple bond alternation exists in the linear carbon chain and single ring.

When the ring has a branched chain, the change of



Table 3 Vibrational frequencies of the ground state isomers of C20H3

Isomer vlow/cm－1 vC≡C/cm－1 v strong/cm－1 [IR inten./

(km•mol－1)] Isomer vlow/cm－1 vC≡C/cm－1

v strong/cm－1 [IR inten./ (km•mol－1)]

A1 11 (b2) 2051 (a1) 3491 (a1 410) E3 24 (a') 2036 (a') 3491 (a' 215)

A2 11 (a') 2052 (a') 3490 (a' 431) E4 23 (a") 2049 (a') 3493 (a' 228)

A3 10 (a') 2013 (a') 3489 (a' 437) F1 20 (a") 2061(a') 3492 (a' 259)

A4 10 (a') 2032 (a') 3489 (a' 403) F2 19 (a') 2052 (a') 3492 (a' 249)

B1 46 (a') 2023 (a') 579 (a' 49) F3 19 (a') 2096 (a') 3492 (a' 250)

B2 48 (a") 2035 (a') 1567 (a' 85) F4 20 (b2) 2025 (b2) 3492 (a1 243)

B3 38 (a") 2020 (a') 1025 (a' 79) GI 17 (a') 2043 (a') 3491 (a' 265)

B4 49 (a') 2059 (a') 1905 (a' 97) G2 16 (a') 2027 (a') 3491 (a' 261)

C1 41 (a") 2048 (a') 3492 (a' 141) G3 17 (a') 2038 (a') 3492 (a' 258)

C2 40 (a") 2038 (a') 3492 (a' 143) G4 16 (a') 2097 (a') 3492 (a' 266)

C3 44 (a") 2037 (a') 3493 (a' 133) H1 145 — 491 (68)

C4 39 (a") 2041 (a') 3492 (a' 145) H2 144 — 491 (78)

D1 26 (a") 2042 (a') 3493 (a' 196) H3 138 — 492 (118)

D2 29 (a") 2047 (a') 3493 (a' 188) H4 140 — 493 (111)

D3 27 (a") 2063 (a') 3493 (a' 189) I1 377 (a") — 3117 (a' 65)

D4 26 (a") 2037 (a') 3492 (a' 184) I2 351 — 725 (82)

E1 24 (a') 2039 (a') 3492 (a' 225) I3 166 (a") — 704 (a' 62)

E2 24 (a") 2039 (a') 3493 (a' 221) I4 354 — 707 (94)

vibrational frequency is not large. Because the eight-een-membered ring isomers have the character of single and triple bond alternation, the stretching vibration model of C≡C bond and the lowest frequency near 40 cm－1, which is the bending of the whole ring, exist in the structures.

The stretching vibration model of C≡C bond also exists in the 16-, 14-, 12-, 10-membered ring isomers. Obviously, the single and triple bond alternation exists in the linear carbon chain and single ring. They all have the lowest frequency. The vibrational way of the lowest frequency of the sixteen-membered ring is the bending of the whole ring and the vibrational frequency is be-tween 26 and 29 cm－1. The vibrational model of the lowest frequency of the fourteen-membered ring is the bending of the whole ring, too. It is either 23 or 24 cm－1. But the vibrational way of the lowest frequency of the twelve- and ten-membered rings is the bending of the ring and linear chain. They are 19 or 20 cm－1 and 16 or 17 cm－1, respectively. This is different from other groups. Because the linear carbon chains of the twelve- and ten-membered rings are very long, the two parts of the ring and chain have interaction. It suggests that the lowest frequency decreases as the single ring becomes smaller.

As shown in Table 3, the eighteen-membered, six-teen-membered, fourteen-membered, twelve-membered and ten-membered ring isomers have the strongest ab-sorptions at about 3500 cm－1, which have the strongest IR activity and are the stretching mode of the ≡C—H. Thus, the isomer that has the linear chain has the stretching mode of the ≡C—H. Also it indicates that

the stretching mode of the ≡C—H exists in the group with a linear chain. The bonds of C≡C exist in the lin-ear chain. The strongest absorptions arise from the stretching mode of the ring for the twenty-membered ring. The bowl-like isomers have the strong absorption mode, which arises from the whole bowl. The stretching mode of the three C—H bonds of I1 has the strongest IR activity. The strong IR absorptions of other three iso-mers arise from the bending mode in the cage.

Because the bowl-like and cage-like isomers do not have the linear chain and single ring, the lowest fre-quency can not be obtained. The stretching vibration model of C≡C bond disappears because they do not own the single and triple bond alternation structures.

Local strain energy around the edge of bowl-like C20

The energies of bowl-like isomer of C20 and C20H3 have been obtained. Their total energies are －761.49159 and －763.46855 hartree, respectively. C20H3 is more stable than C20. In this case, it must be assumed that the hydrogenation reaction takes place at hexagons, leading to that relaxation of the strain around the edge of hex-acene belt of C20. In order to gain insight into the re-laxation process through hydrogenation, we devised the reaction to predict the released energy ∆Er as shown in Figure 14.22

The released energy ∆Er due to relaxation of the strain by hydrogenation is given by

∆Er ＝ 2Etot(C20H3) ＋ 3Etot(CHCH) － [2Etot(C20) ＋

3Etot(H2CCH2)]



Figure 14 Hydrogenation reaction of bowl-like C20.

We can obtain the result with ∆Er＝－4.58 eV, which is the released energy due to relaxation of the strain by hydrogenation.

Conclusion

The most stable isomer of C20H3 is the bowl-like structure with C1 symmetry, in which the three hydro-gen atoms locate on the edge carbon atoms, and the two hydrogen atoms are neighbouring and the third one has a two-carbon interval to the neighbouring hydrogen. It is important to build the isomers of the single ring structure and cage structure for larger series of CnH3 radicals. The most stable isomer of each group has neighbouring position H atom except for the ten-membered ring. Open chain and single ring isomers all have single-triple bond alternation polyacetylenic structures. The character has important influence on stability. We note that the open chain and single ring isomers all have a lowest frequency in the 10—50 cm－1 region as C7H3, C9H3, C11H3 and C13H3. In addition, hydrogenation can relax the strain and make the isomer more stable. We can obtain the result with ∆Er＝－4.58 eV, which is the released energy due to relaxation of the strain by hydrogenation.

References

1 Douglas, A. E. Nature (London) 1977, 269, 130. 2 Fulara, J.; Lessen, D.; Freivogel, P.; Maier, J. P. Nature 2002,

366, 332. 3 Schmidt, T. W.; Ding, H.; Boguslavskiy, A. E.; Pino, T.;

Maier, J. P. J. Phys. Chem. A 2003, 107, 6550. 4 McCarthy, M. C.; Thaddeus, P. Chem. Soc. Rev. 2001, 30,

177. 5 Ball, C. D.; McCarthy, M. C.; Thaddeus, P. J. Chem. Phys.

2000, 112, 10149. 6 Pino, T.; Ding, H.; Guthe, F.; Maier, J. P. J. Chem. Phys.

2001, 114, 2208. 7 Turner, B. E.; Herbst, E.; Terzieva, R. Astrophys. J. Suppl. S

2000, 126, 427. 8 Guelin, M.; Cernicharo, J.; Travers, M. J.; McCarthy, M. C.;

Gottlieb, C. A.; Thaddeus, P.; Ohishi, M.; Saito, S. Astron. Astrophys. 1997, 317, L1.

9 Zhang, C.; Cao, Z.; Zhang, Q. Chem. Res. Chin. Univ. 2003, 19, 454.

10 Grutter, M.; Wyss, M.; Fulara, J.; Maier, J. P. J. Phys. Chem. A 1998, 102, 9785.

11 Zhang, C.; Cao, Z.; Wu, H.; Zhang, Q. Int. J. Quantum Chem. 2004, 98, 299.

12 Mebel, A. M.; Lin, S. H.; Yang, X. M.; Lee, Y. T. J. Phys. Chem. A 1997, 101, 6781.

13 Schmidt, T. W.; Boguslavskiy, A. E.; Pino, T.; Ding, H.; Maier, J. P. Int. J. Mass Spec. 2003, 228, 647.

14 Flalkov, A. B.; Homann, K.-H. Combust. Flame 2001, 127, 2076.

15 Schnaiter, M.; Henning, T.; Mutschke, H.; Kohn, B.; Ehbrecht, M.; Huisken, F. Astrophys. J. 1999, 519, 687.

16 Tanaka, K.; Sumiyoshi, Y.; Ohshima, Y.; Endo, Y.; Kawa-guchi, K. J. Chem. Phys. 1997, 107, 2728.

17 Ding, H.; Pino, T.; Gűthe, F.; Maier, J. P. J. Am. Chem. Soc. 2003, 125, 14626.

18 Zhang, C. J. Chem. Phys. 2004, 121, 8212. 19 Jone, R. O. J. Chem. Phys. 1999, 110, 11. 20 Frisch, M. J.; Trucks, G. W.; Schegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Mont-gomery, J. A. Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Peterson, G. A.; Ayala, P. Y.; Cui, Q.; Moro-kuma, K.; Malick, D. K.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Sefanov, B. B.; Liu, G.; Li-ashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Mar-tin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Chahacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Po-ple, J. A. Gaussian 98, Gaussian, Inc., Pittsburgh, PA, 1998.

21 Zhang, C.; Xu, X.; Wu, H.; Zhang, Q. Chem. Phys. Lett. 2002, 364, 213.

22 Ito, A.; Monobe, T.; Yoshii, T.; Tanaka, K. Chem. Phys. Lett. 2000, 330, 281.

(E0704205 ZHU, H. F.; FAN, Y. Y.)

Structure and Stability of C20H3 Radical

Documents

Transcript of Structure and Stability of C20H3 Radical