Nonpolar nitrous oxide dimer: fundamentals of the mixed 14N2O–15N2O dimer and new combination bands of (14N2O)2 and (15N2O)2 involving the Bu intermolecular bend

Abstract

Spectra of the nonpolar nitrous oxide dimer in the region of the N₂O ν₁ fundamental band are observed in a pulsed supersonic slit jet expansion probed with a tunable diode laser. Four bands are analysed: two fundamentals of the mixed ¹⁴N₂O–¹⁵N₂O dimer and combination bands involving the intermolecular disrotation of the monomers (B_u intermolecular bend) for both (¹⁴N₂O)₂ and (¹⁵N₂O)₂. Because the determination of this intermolecular frequency relies on the experimentally unknown frequency of the (forbidden) symmetric fundamental, we used previously published ab initio results and their proximity to our experimental values to assign the upper state of the combination bands. The resulting intermolecular disrotation frequencies are 42.3(1.0) and 41.6(1.0) cm⁻¹ for the (¹⁴N₂O)₂ and (¹⁵N₂O)₂, respectively. This represents the first observation of the mixed ¹⁴N₂O–¹⁵N₂O dimer, and the direct determination of a second intermolecular frequency for the nonpolar (N₂O)₂.