High-Resolution Spectroscopy and Structure of Heavy Carbon Subchalcogenides: Tricarbon Selenide, C3Se

Linear tricarbon selenide, C3Se, has been studied spectroscopically for the first time using a combination of high-resolution infrared and microwave techniques. Probing laser ablation products from carbon-selenium targets in a free jet expansion with He, initial spectroscopic detection was accomplished in the infrared at a wavelength of 5 mu m in search of the nu(1) vibrational fundamental. Along with the band of the most abundant isotopic species (C3Se)-Se-80 found centered at about 2039 cm(-1), the corresponding bands of the (C3Se)-Se-82, (C3Se)-Se-78, (C3Se)-Se-76, and (C3Se)-Se-77 isotopologues were also detected. Pure rotational spectra of the five C3Se isotopologues in the 8-18 GHz frequency range were observed in a supersonic jet expansion using chirped-pulse microwave spectroscopy of the discharge products of selenophene, c-C4H4Se. Spectroscopic analyses were guided by results from high-level quantum-chemical calculations carried out at the coupled-cluster level of theory using large correlation-consistent basis sets. Using the experimentally derived ground-state rotational constants of five isotopologues and calculated zero-point vibrational corrections, an accurate semiexperimental equilibrium carbon-selenium bond length is derived.