Wagner C J, Galvin T C, Eden J G
Laboratory for Optical Physics and Engineering, Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, USA.
J Chem Phys. 2014 Jun 28;140(24):244312. doi: 10.1063/1.4884606.
Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ∼160 nl. Transient suppression of Xe2 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g)) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω(g) ← a(3)Σ(+)(u)(1(u), O(-)(u)) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed Ω(g) ← a(3)Σ(+)(u) transitions involving Ω = 0(±),1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p(6) (1)S0) + Xe(5p(5) 6p) and built on a predominantly A(2)Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1(g) ← 1(u), O(±)(u) absorptive transitions are determined to be Te = 13,000 ± 150 cm(-1), ω'(e) = 120 ± 10 cm(-1), ω'(e)x'(e) = 1.1 ± 0.4 cm(-1), De = 3300 ± 300 cm(-1), and ΔR(e) = R'(e) = R''(e) = 0.3 ± 0.1 Å which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1g and (3)O(+)(g) states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999, associated with Xe2 Rydberg states derived from the Xe(7p) orbital.
在体积约为160 nl的脉冲氙微等离子体余辉中，通过激光光谱法在545 - 555 nm和675 - 800 nm光谱区域观测到了小核间距（R < 4.0 Å）下氙二聚体的束缚态←束缚态跃迁。由分子的Ω(g) ← a(3)Σ(+)(u)(1(u), O(-)(u)) [里德堡←里德堡] 跃迁的激光激发所诱导的真空紫外区（~172 nm）中Xe2 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g))发射的瞬态抑制，证实了720至770 nm之间结构的存在（Killeen和Eden [《化学物理杂志》84, 6048 (1986)] 报道），但也揭示了延伸至800 nm以上波长的红移振动带。基于对涉及Ω = 0(±),1 gerade里德堡态的假定Ω(g) ← a(3)Σ(+)(u)跃迁的弗兰克 - 康登因子计算的光谱模拟表明，对观测光谱起主要作用的上能级是一个Ω = 1态，在分离原子极限下，与Xe(5p(6) (1)S0) + Xe(5p(5) 6p)相关，并建立在主要为A(2)Π3/2g分子离子核心上。具体而言，1(g) ← 1(u), O(±)(u)吸收跃迁的上能级的光谱常数确定为Te = 13,000 ± 150 cm(-1)，ω'(e) = 120 ± 10 cm(-1)，ω'(e)x'(e) = 1.1 ± 0.4 cm(-1)，De = 3300 ± 300 cm(-1)，以及ΔR(e) = R'(e) = R''(e) = 0.3 ± 0.1 Å，这与Jonin和Spiegelmann [《化学物理杂志》117, 3059 (2002)] 为Xe2的(5)1g和(3)O(+)(g)态所开发的赝势空穴 - 粒子形式理论的理论预测总体一致。这些光谱展现出最广泛的振动发展，并为小R（<4 Å）下任何稀有气体二聚体迄今为止观测到的首次分子核心切换跃迁提供了证据。相对于1986年和1999年报道的数据，绿色区域（545 - 555 nm）的实验也提供了与源自Xe(7p)轨道的Xe2里德堡态相关的改进吸收光谱。
