Millimeter/sub-mm spectroscopy of the CrBr radical in the high spin X6Σ+ state.

T J Herman,L M Ziurys,J P Keogh

doi:10.1063/1.5125013

Abstract

The millimeter/submillimeter spectrum of the CrBr radical has been recorded in the frequency range of 220-300 GHz using direct absorption techniques, utilizing a new instrumental design. This study is the first spectroscopic investigation of this radical species by any method. CrBr was synthesized in a DC discharge by the reaction of chromium vapor, produced in a Broida-type oven, with Br2CH2 in argon. Six to nine rotational transitions were measured for four isotopologues of this molecule in their natural abundances, 52Cr79Br, 52Cr81Br, 53Cr79Br, and 53Cr81Br. Each transition was found to consist of six distinct fine structure components, indicating a 6Σ+ ground electronic state, as observed for CrF and CrCl. Lines originating in the v = 1 and 2 vibrational states were recorded for 52Cr79Br and 52Cr81Br as well. The spectra were analyzed using a Hund's case (b) Hamiltonian, and rotational, spin-spin, and spin-rotation parameters were determined. The third-order spin-rotation constant γs and the fourth order spin-spin term θ were necessary for the analysis; these parameters are thought to play a role in states with high multiplicities. Equilibrium parameters were also derived for the CrBr; a bond length of re = 2.337 282 (30) Å and a vibrational constant of ωe ≅ 300 cm-1 were determined. The sign and magnitude of the spin-spin and spin-rotation constants suggest the presence of nearby 4Π and 6Π excited states in CrBr, lying ∼9000 cm-1 above the ground state. The new instrument design, employing more compact, free-space optics utilizing an offset ellipsoidal mirror, facilitated these measurements.

Highlights

IntroductionChromium halides have been of chemical interest for decades, in organic synthesis
The third-order spin-rotation constant γs and the fourth order spin-spin term θ were necessary for the analysis; these parameters are thought to play a role in states with high multiplicities
Chromium halides have been of chemical interest for decades, in organic synthesis

Summary

Introduction

Chromium halides have been of chemical interest for decades, in organic synthesis. The chromium salts CrCl2 and CrCl3 have proven to be useful catalysts, enabling, for example, the cleavage and cross coupling of unactivated chemical bonds, such as C–O and C–N bonds, in conjunction with powerful Grignard reagents.. It has been shown that such salts, combined with alkyl halides, can lead to ortho-alkylated compounds by catalytic cleavage of unactivated C–H bonds at ambient temperature.. It has been shown that such salts, combined with alkyl halides, can lead to ortho-alkylated compounds by catalytic cleavage of unactivated C–H bonds at ambient temperature.2 Another useful catalyst is CrBr3, commonly employed in the polymerization of olefins.. The 2D material, CrBr3, is the first ferromagnetic semiconductor ever discovered.. The 2D material, CrBr3, is the first ferromagnetic semiconductor ever discovered.6 It has been incorporated into van der Waals heterostructures with interesting tunneling properties, in particular when layered with graphene. The chromium salts CrCl2 and CrCl3 have proven to be useful catalysts, enabling, for example, the cleavage and cross coupling of unactivated chemical bonds, such as C–O and C–N bonds, in conjunction with powerful Grignard reagents. More recently, it has been shown that such salts, combined with alkyl halides, can lead to ortho-alkylated compounds by catalytic cleavage of unactivated C–H bonds at ambient temperature. Another useful catalyst is CrBr3, commonly employed in the polymerization of olefins. Chromium halides have some interesting structural properties. The crystal arrangement of CrBr2 appears to consist of Cr2+ ions surrounded by unusual distorted octahedra of bromine ions. The 2D material, CrBr3, is the first ferromagnetic semiconductor ever discovered. It has been incorporated into van der Waals heterostructures with interesting tunneling properties, in particular when layered with graphene.

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