McCarthy M C, Tamassia F, Woon D E, Thaddeus P
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
J Chem Phys. 2008 Nov 14;129(18):184301. doi: 10.1063/1.3002914.
The rotational spectrum of the triatomic free radical SiOH in its X (2)A(') ground electronic state has been observed in a supersonic molecular beam by Fourier transform microwave spectroscopy. The fundamental (1(0,1)-->0(0,0)) transition has been detected for normal SiOH and for three rare isotopic species: (30)SiOH, Si(18)OH, and SiOD. The same transition has also been observed in two of three excited vibrational states, v(2) and v(3), for the most abundant species. Precise spectroscopic constants, including those that describe the effective spin doubling and hydrogen hyperfine structure, have been derived for each isotopic species or vibrational state. To complement the laboratory work, theoretical calculations of the structure, dipole moment, and energies of the X (2)A(') and low-lying 1 (2)A(") states have also been undertaken at the coupled cluster level of theory. In agreement with theoretical predictions, we conclude from the hyperfine constants that SiOH is a best described as a pi-type radical, with the unpaired electron localized on a p orbital on the silicon atom. Assuming a bond angle of 118.5 degrees , the Si-O bond length is 1.647(2) A and the O-H bond length is 0.969(4) A.
利用傅里叶变换微波光谱技术，在超声分子束中观测到了处于X (2)A(')基电子态的三原子自由基SiOH的转动光谱。已检测到正常SiOH以及三种稀有同位素物种（(30)SiOH、Si(18)OH和SiOD）的基频（1(0,1)-->0(0,0)）跃迁。对于最丰富的物种，在三个激发振动态中的两个（v(2)和v(3)）也观测到了相同的跃迁。已为每种同位素物种或振动态推导了精确的光谱常数，包括描述有效自旋加倍和氢超精细结构的常数。为补充实验室工作，还在耦合簇理论水平上对X (2)A(')和低激发1 (2)A(")态的结构、偶极矩和能量进行了理论计算。与理论预测一致，我们从超精细常数得出结论，SiOH最好被描述为π型自由基，未成对电子定域在硅原子的p轨道上。假设键角为118.5度，Si - O键长为1.647(2) Å，O - H键长为0.969(4) Å。
