Examining the transition metal hydrosulfides: the pure rotational spectrum of CuSH (X˜1A′)

doi:10.1016/j.cplett.2004.10.146

Chemical Physics Letters

Volume 401, Issues 1–3, 1 January 2005, Pages 211-216

https://doi.org/10.1016/j.cplett.2004.10.146 Get rights and content

Abstract

The pure rotational spectrum of copper hydrosulfide, CuSH, has been recorded using millimeter/sub-millimeter direct absorption methods. Both copper isotopomers and their deuterated analogs were observed. The molecules were synthesized by the reaction of H₂S or D₂S with copper vapor in a dc discharge. For all four isotopomers, multiple transitions were measured, each exhibiting extensive K_a ladder structure and signifying that CuSH is a near-prolate asymmetric top. Rotational parameters were determined for the four species, from which a structure has been derived. The Cu–S–H bond angle was found to be 93°, similar to other metal hydrosulfides and H₂S, rather than CuOH.

Introduction

The formation of metal–OH bonds is important in a wide range of scientific fields, including electrochemistry, corrosion phenomena and in biological processes [1], [2]. As a consequence, the spectra of many alkali and alkaline earth monohydroxides, as well as AlOH, have been measured by a variety of techniques [3], [4], [5], [6], [7], [8], [9]. These molecules have been found to be linear or quasilinear in their ground electronic states, and some are known to exhibit large amplitude bending motions [10]. In contrast, transition metal monohydroxides have largely been neglected. Thus far, the spectra of only CuOH and AgOH have been studied [11], [12], [13], [14]. These species have been found to be bent with angles near 108–110°, the tetrahedral angle, suggestive of some sort of orbital hybridization.

The sulfur analogs of the metal monohydroxides, the hydrosulfides MSH, have varied chemical applications, from the creation of metalloenzymes to industrial hydrodesulfurization [15]. To date, only alkali and alkaline earth-bearing molecules of this type have been investigated spectroscopically [16], [17], [18], [19], [20]. These species have all been discovered to be bent with an angle near 90°. The structural variations between the alkali/alkaline earth monohydroxides and the monohydrosulfides probably reflect the differences in electronegativity, orbital energies and atomic radius of oxygen relative to sulfur.

In this Letter, we present the first gas-phase spectroscopic study of a transition metal hydrosulfide. The pure rotational spectrum of CuSH in its ${\tilde{X}}^{1} A^{'}$ ground electronic state was recorded using millimeter/sub-millimeter direct absorption techniques. Spectra of the deuterium isotopomer, CuSD, and the less abundant copper species, ⁶⁵CuSH and ⁶⁵CuSD, were also measured. These data clearly indicate that CuSH is bent. Here, we describe our results and compare the properties of CuSH with other metal hydrosulfides and hydroxides.

Section snippets

Experimental

The rotational spectra of CuSH and its isotopomers were measured using one of the millimeter-wave spectrometers of the Ziurys group, which is described elsewhere [21]. Briefly, the instrument consists of a Gunn oscillator/Schottky diode multiplier frequency source, a gas cell in which the radiation is propagated quasi-optically, and an InSb bolometer detector. Phase-sensitive detection is achieved by modulating the source and signals are detected at 2f.

CuSH was produced by reacting copper vapor

Results

Because CuSH had not been studied previously by experiment or theory, a bent structure was assumed, which results in an a-type pattern. An effective B value of B + C/2 ∼ 5276 MHz was estimated, which turned out to be quite close to the actual B_eff of 5274 MHz. Consequently, lines originating from CuSH were found after a few hundred MHz of scanning. However, in order to identify harmonic relationships among the K_a asymmetry components, approximately 6 B_eff in frequency (or ∼32 GHz) were continuously

Analysis

All four data sets of CuSH were analyzed using an S-reduced Hamiltonian, which was incorporated into SPFIT, a non-linear least-squares code developed by Pickett [22]. The resulting spectroscopic constants for the four isotopomers are given in Table 3. The individual rms values of the fits lie in the range 27–38 kHz. Nine to ten constants were required to fit each molecule – a much smaller number of parameters than those used for LiSH, SrSH, BaSH [18], [19], [20]. Only two to three sixth-order

Discussion

This study has clearly established that CuSH has a bent geometry with an angle near 93°. This angle differs significantly from that in CuOH, which is near 110°. The tetrahedral angle is 109.5°; therefore, it appears that CuOH bonds via sp³ hybridization of the oxygen orbitals, in analogy to water. CuSH, on the other hand, seems to bond through simple p-orbitals, similar to H₂S, hence the near 90° angle. Thus, the substitution of the oxygen atom with sulfur significantly alters the nature of the

Acknowledgement

This research is supported by NSF Grant CHE-04-11551.

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The determination of the molecular structures, bonding, and physical properties of the simple MSH species is challenging, as the monomeric metal hydrosulfides are usually short-lived transient species of high reactivity. Only CuSH has been the subject of pure-rotational and rotationally-resolved electronic spectroscopic studies until 2012 [18–20]. These studies showed that CuSH was strongly bent (∠(CuSH) = 93°) in its electronic ground state as similar to the main-group metal hydrosulfides.
The equilibrium structure, spectroscopy constants, and anharmonic force field of silver hydrosulfide (AgSH) have been calculated at B3P86, B3PW91 and MP2 methods employing two basis sets, TZP and QZP, respectively. The calculated geometries, ground state rotational constants, harmonic vibrational wave numbers, and quartic and sextic centrifugal distortion constants are compared with the available experimental and theoretical data. The equilibrium rotational constants, fundamental frequencies, anharmonic constants, and vibration-rotation interaction constants, Coriolis coupling constants, cubic and quartic force constants are predicted. The calculated results show that the MP2/TZP results are in good agreement with experiment observation and are also an advisable choice to study the anharmonic force field of AgSH.
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Resonance-enhanced multiphoton ionization (REMPI) spectra of laser-ablated copper atoms entrained in a supersonic free jet expansion are reported. Depending on the ionization scheme employed, and the conditions under which the copper atoms are produced, very different spectra are produced, which are discussed. In some circumstances, high proportions of metastable atoms survive the ablation and expansion process and are clearly seen in the spectra. The spectroscopic transitions for the observed lines are identified, and it is noted that some caution is merited in the assumption that only ground state copper atoms are present following laser ablation.
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The rotational spectrum of AgSH was observed in a dc discharge absorption cell in the range of 192–312 GHz. The AgSH molecule was generated in a reaction of H₂S with Ag sputtered from silver sheets lining a stainless-steel cathode. The spectra of ¹⁰⁷AgSH, ¹⁰⁹AgSH, ¹⁰⁷AgSD, and ¹⁰⁹AgSD correspond to that of a near-prolate asymmetric top. Molecular constants were determined by least-squares method. A harmonic force field analysis for AgSH combined with its copper analog, CuSH, enabled the determination of the $r_{z}$ structure of both molecules. AgSH and CuSH molecules possess highly bent structures indicating considerable covalent character.
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Microwave (MW) spectroscopy has mostly been—and sometimes even by spectroscopists still is—considered to be a tool to obtain molecular structures. The development of Fourier transform microwave (FTMW) spectroscopy and, most notably, its combination with supersonic-jet expansion techniques allow for challenging investigations of chemically and physically interesting molecular systems. The combination of Fourier transform MW (FTMW) spectroscopy with supersonic-jet expansions allowed the study of the rotational spectra of weakly bound molecular complexes. These are, among others, in situ prepared molecular species such as radicals, ions, and other transient species, generated by combining an electrical discharge, laser ablation, or laser photolysis, and highly dynamical systems including weakly bound molecular complexes. From these latter systems, information on nonbonding intermolecular interactions and on the internal dynamics is easily obtained. Many chemical problems, difficult to unravel with other techniques, were solved only by rotational spectroscopy experiments on supersonic jets. The widely unexplored interactions in the intermediate regime between bonding and nonbonding, molecular recognition, molecular aggregation, and many more are investigated with these techniques without having to rely on ab initio calculations—their support is of great help both in guiding spectroscopic searches and in interpreting the spectra.

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Chemical Physics Letters

Abstract

Introduction

Section snippets

Experimental

Results

Analysis

Discussion

Acknowledgement

References (24)

J. Mol. Spectrosc.

Chem. Phys.

Chem. Phys. Lett.

J. Mol. Spectrosc.

Coord. Chem. Rev.

Chem. Phys. Lett.

Chem. Phys. Lett.

J. Mol. Spectrosc.

J. Mol. Spectrosc.

J. Am. Chem. Soc.

Inorg. Chem.

Can. J. Chem.

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