Steill Jeffrey D, Oomens Jos, Eyler John R, Compton Robert N
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600, USA.
J Chem Phys. 2008 Dec 28;129(24):244302. doi: 10.1063/1.3036977.
Resonantly enhanced multiple photon dissociation of gas-phase SF(6) (-) and SF(5) (-) is studied using tunable infrared light from the FELIX free electron laser. The photodissociation spectrum of the sulfur hexafluoride anion, producing SF(5) (-), is recorded over the spectral range of 250-1650 cm(-1). The infrared multiple photon dissociation cross section exhibits a strong, broad resonance enhancement at 675 cm(-1) in agreement with the calculated value of nu(3), one of the two IR-active fundamental vibrational modes predicted for the O(h)-symmetry ion. Much weaker absorption features are observed in the spectral region of 300-450 cm(-1) as well as at 580 cm(-1) that are not easily assigned to the other IR-active fundamental of SF(6) (-) since these resonances are observed at a much higher energy than the calculated values for the IR-active nu(4) mode. The potential role of binary combination bands is considered. Photodissociation from the sulfur pentafluoride anion produced only F(-), but photodetachment was also observed through SF(6) associative electron capture. The IR multiple photon dissociation spectrum of SF(5) (-) shows multiple resonances within the region of 400-900 cm(-1) and agreement with calculations is clear, including the observation of three fundamental frequencies: nu(1) at 780 cm(-1), nu(7) at 595 cm(-1), and nu(8) at 450 cm(-1). Comparisons of the measured frequencies with ab initio and density functional theory calculations confirm an SF(5) (-) anion of C(4v) symmetry. Similar comparisons for SF(6) (-) are not inconsistent with an anion of O(h) symmetry.
利用来自FELIX自由电子激光的可调谐红外光,研究了气相SF(6) (-)和SF(5) (-)的共振增强多光子解离。在250 - 1650 cm(-1)的光谱范围内记录了产生SF(5) (-)的六氟化硫阴离子的光解离光谱。红外多光子解离截面在675 cm(-1)处呈现出强烈、宽广的共振增强,这与计算得到的ν(3)值一致,ν(3)是预测的O(h)对称离子的两个红外活性基本振动模式之一。在300 - 450 cm(-1)光谱区域以及580 cm(-1)处观察到了弱得多的吸收特征,这些特征不容易归属于SF(6) (-)的另一个红外活性基本模式,因为这些共振出现在比红外活性ν(4)模式计算值高得多的能量处。考虑了二元组合带的潜在作用。五氟化硫阴离子的光解离仅产生F(-),但通过SF(6)缔合电子俘获也观察到了光剥离。SF(5) (-)的红外多光子解离光谱在400 - 900 cm(-1)区域显示出多个共振,与计算结果的一致性很明显,包括观察到三个基本频率:780 cm(-1)处的ν(1)、595 cm(-1)处的ν(7)和450 cm(-1)处的ν(8)。将测量频率与从头算和密度泛函理论计算结果进行比较,证实了C(4v)对称的SF(5) (-)阴离子。对SF(6) (-)进行的类似比较与O(h)对称的阴离子并不矛盾。