A global potential energy surface and dipole moment surface for silane

Abstract

A new nine-dimensional potential energy surface (PES) and dipole moment surface (DMS) for silane have been generated using high-level \textit{ab initio} theory. The PES, CBS-F12$^{\,\mathrm{HL}}$, reproduces all four fundamental term values for $^{28}$SiH$_4$ with sub-wavenumber accuracy, resulting in an overall root-mean-square (rms) error of $0.63{\,}$cm$^{-1}$. The PES is based on explicitly correlated coupled cluster calculations with extrapolation to the complete basis set limit, and incorporates a range of higher-level additive energy corrections to account for core-valence electron correlation, higher-order coupled cluster terms, and scalar relativistic effects. Systematic errors in computed intra-band rotational energy levels are reduced by empirically refining the equilibrium geometry. The resultant Si-H bond length is in excellent agreement with previous experimental and theoretical values. Vibrational transition moments, absolute line intensities of the $\nu_3$ band, and the infrared spectrum for $^{28}$SiH$_4$ including states up to $J=20$ and vibrational band origins up to $5000{\,}$cm$^{-1}$ are calculated and compared with available experimental results. The DMS tends to marginally overestimate the strength of line intensities. Despite this, band shape and structure across the spectrum are well reproduced and show good agreement with experiment. We thus recommend the PES and DMS for future use.