Tang Sheunn-Jiun, Chou Yung-Ching, Lin Jim Jr-Min, Hsu Yen-Chu
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan, Republic of China.
J Chem Phys. 2006 Oct 7;125(13):133201. doi: 10.1063/1.2199827.
Forty three vibronic levels of C2H2+, X 2Pi u, with upsilon4 = 0-6, upsilon5 = 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 A1Au, 4nu3 (K = 1-2), 5nu3 (K = 1), nu2+4nu3 (K = 0), and 47,206 cm(-1) (K = 1) levels of C2H2. Seven of the trans-bending levels of C2H2+ (upsilon4 = 0-3, K = 0-2) had been reported previously by Pratt et al. [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 upsilon4 + upsilon5 < or = 2, except for the unobserved upper (2Pi u component of the 2nu4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm(-1). The vibronic coupling parameter epsilon5 (about whose magnitude there has been controversy) was determined to be -0.0273(7). 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 upsilon4 + upsilon5 = 3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with upsilon4 + upsilon5 < or = 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 Sigmau components of the nu4 + 2nu5 combination level. The ionization potential of C2H2 (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) (3sigma).
已在转动分辨率下记录了处于零点能级之上0 - 3520厘米⁻¹能量范围内的C₂H₂⁺，X²Πᵤ，υ₄ = 0 - 6、υ₅ = 0 - 3且K = 0 - 4的43个振转能级。这些能级通过双共振观测，采用1 + 1'双色脉冲场电离零动能光电子能谱。中间态是从C₂H₂的A¹Δᵤ、4υ₃（K = 1 - 2）、5υ₃（K = 1）、υ₂ + 4υ₃（K = 0）以及47206厘米⁻¹（K = 1）能级中选取的单个振转能级。C₂H₂⁺的七个反式弯曲能级（υ₄ = 0 - 3，K = 0 - 2）先前已由普拉特等人报道过[《化学物理杂志》99, 6233 (1993)]；我们对这些能级的结果与他们的结果吻合得很好。已进行了全面分析，包括反式和顺式弯曲振动的伦纳 - 泰勒效应及振动非谐性。最低的16个振转能级（由υ₄ + υ₅≤2的完整能级集合组成，除了未观测到的2υ₄泛音的较高（²Πᵤ分量））的转动结构可以用16个参数通过最小二乘法拟合，均方根偏差为0.21厘米⁻¹。振转耦合参数ε₅（其大小存在争议）被确定为 - 0.0273(7)。对于较高的振转能级，需要一个额外的参数r₄₅来考虑两个弯曲流形之间的达林 - 丹尼森共振。然后几乎所有观测到的υ₄ + υ₅ = 3和4多重态的能级（约为预测数量的一半）都可以被归属。在对υ₄ + υ₅≤5的39个振转能级进行最终拟合时，使用20个参数获得了0.34厘米⁻¹的均方根偏差。一个有趣的发现是，洪德自旋耦合情况（a）和（b）都出现在υ₄ + 2υ₅组合能级的Σᵤ分量中。发现C₂H₂的电离势（从基态的最低转动能级到阳离子的最低转动能级）为91953.77±0.09厘米⁻¹（3σ）。
