Ab Initio Potential Energy Surfaces for Both the Ground ( ) and Excited ( ) Electronic States of HSiBr and the Absorption and Emission Spectra of HSiBr/DSiBr
Ab Initio potential energy surfaces for the ground ( ) and excited ( ) electronic states of HSiBr were obtained by using the single and double excitation coupled-cluster theory with a noniterative perturbation treatment of triple excitations and the multireference configuration interaction with Davidson correction, respectively, employing an augmented correlation-consistent polarized valence quadruple zeta basis set. The calculated vibrational energy levels of HSiBr and DSiBr of the ground and excited electronic states are in excellent agreement with the available experimental band origins. In addition, the absorption and emission spectra of HSiBr and DSiBr were calculated using an efficient single Lanczos propagation method and are in good agreement with the available experimental observations. 1. Introduction Silylenes and its halogenated analogs are important reactive intermediates in the chemical vapor deposition of silicon thin films [1] and plasma etching process [2]. The identification and quantification of such intermediates could help make these processes more efficient, so that they have attracted much attention in experimental and theoretical studies [3–17]. However, because these radicals are typically short-lived and highly reactive, it is difficult to monitor them. Due to the lack of comprehensive spectroscopic signatures for these species, the detailed mechanism of such semiconductor growth processes is still not fully understood. In this work, we focus on the monobromosilylene (HSiBr) system, which was first detected by Herzberg and Verma in 1964 [3]. Both absorption and emission spectra of HSiBr in the 410–600？nm were obtained by flash photolysis of SiH3Br. The vibrational fundamentals and geometries for both the ground and excited states were confirmed after vibrational and rotational analyses of the spectra. Although no spin splittings were observed, the occurrence of subbands with and led them to assume that the electronic transition was triplet-singlet. Subsequently in 1965, these electronic transitions were confirmed to be by Hougen and Watson via an “axis-switching” mechanism [4]. The spectra of the system of jet-cooled HSiBr and its deuterated analog were obtained about 15 years ago by Harjanto et al. [8] using pulsed electric discharge techniques, and the structures for the ground and excited states were determined from the rotational analyses of the band. Later in 2001, 26/51 ground state vibrational levels of HSiBr/DSiBr were observed by Hostutler et al. [13] from the single vibronic level dispersed fluorescence spectra of
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