TY - JOUR

T1 - The bending vibrational levels of the acetylene cation

T2 - A case study of the Renner-Teller effect in a molecule with two degenerate bending vibrations

AU - Tang, Sheunn Jiun

AU - Chou, Yung Ching

AU - Lin, Jim Jr Min

AU - Hsu, Yen Chu

N1 - Funding Information:
The authors thank the Academia Sinica and the National Science Council of Taiwan, R.O.C. (Grant Nos. NSC88-2113-M-001-025 and NSC89-2113-M-001-078) for financial support. One of the authors (Y.-C.C.) would like to acknowledge the Academia Sinica for a postdoctoral fellowship. The authors are also grateful to Dr. J. T. Hougen (NIST, Gaithersburg) and Professor A. J. Merer (UBC, Vancouver) for valuable assistance with parts of this work.

PY - 2006

Y1 - 2006

N2 - Forty three vibronic levels of C2 H2+, X̃ Πu2, with 4 =0-6, 5 =0-3, and K=0-4, lying at energies of 0-3520 cm-1 above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+ 1′ two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the Ã Au1, 4 3 (K=1-2), 5 3 (K=1), 2 +4 3 (K=0), and 47 206 cm-1 (K=1) levels of C2 H2. Seven of the trans-bending levels of C2 H2+ (4 =0-3, K=0-2) had been reported previously by Pratt [J. Chem. Phys. 99, 6233 (1993)]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with 4 + 5 ≤2, except for the unobserved upper Πu2 component of the 2 4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm-1. The vibronic coupling parameter ε5 (about whose magnitude there has been controversy) was determined to be - 0.02737. For the higher vibronic levels, an additional parameter, r45, was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the 4 + 5 =3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with 4 + 5 ≤5, an rms deviation of 0.34 cm-1 was obtained using 20 parameters. An interesting finding is that Hund's spin-coupling cases (a) and (b) both occur in the u components of the 4 +2 5 combination level. The ionization potential of C2 H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91 953.77±0.09 cm-1 (3).

AB - Forty three vibronic levels of C2 H2+, X̃ Πu2, with 4 =0-6, 5 =0-3, and K=0-4, lying at energies of 0-3520 cm-1 above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+ 1′ two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the Ã Au1, 4 3 (K=1-2), 5 3 (K=1), 2 +4 3 (K=0), and 47 206 cm-1 (K=1) levels of C2 H2. Seven of the trans-bending levels of C2 H2+ (4 =0-3, K=0-2) had been reported previously by Pratt [J. Chem. Phys. 99, 6233 (1993)]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with 4 + 5 ≤2, except for the unobserved upper Πu2 component of the 2 4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm-1. The vibronic coupling parameter ε5 (about whose magnitude there has been controversy) was determined to be - 0.02737. For the higher vibronic levels, an additional parameter, r45, was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the 4 + 5 =3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with 4 + 5 ≤5, an rms deviation of 0.34 cm-1 was obtained using 20 parameters. An interesting finding is that Hund's spin-coupling cases (a) and (b) both occur in the u components of the 4 +2 5 combination level. The ionization potential of C2 H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91 953.77±0.09 cm-1 (3).

UR - http://www.scopus.com/inward/record.url?scp=33749486806&partnerID=8YFLogxK

U2 - 10.1063/1.2199827

DO - 10.1063/1.2199827

M3 - 期刊論文

AN - SCOPUS:33749486806

SN - 0021-9606

VL - 125

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

IS - 13

M1 - 133201

ER -