Millimeter spectrum and molecular constants of silicon monoxide

A new high-temperature millimeter-wave microwave spectrometer has been constructed and used to measure a wide range of vibrational and rotational states of silicon monoxide. This work results in accurate rest frequencies for all of the intersteller SiO maser transitions that have been observed as well as accurate measurements or predictions of all transitions that are likely to be of astrophysical interest. In addition, the Dunham spectral and potential constants are calculated for the three major isotopic species. For ²⁸Si¹⁶O$: ${Y}₀₁=21787.453(11)$ MHz, ${Y}₁₁={-}151.026(11)$ MHz, ${Y}₂₁=70.5(24)$ kHz, ${Y}₀₂={-}29.38(13)$ kHz, ${a}₀=5.390(22)×{}{10}⁵$ ${cm}^{{-}1}$, ${a}₁={-}2.9899(41)$, ${a}₂=5.7(7)$, ${a}₃={-}9.0(5)$. The calculated equilibrium parameters for $²⁸Si¹⁶O are Bₑ=21787.5(10) MHz, ωₑ=1252.(3) cm^-1, ωₑxₑ=5.96(71) cm^-1, and rₑ=1.50973(4) {}.