Application of continuous wave quantum cascade laser in combination with CIVP spectroscopy for investigation of large organic and organometallic ions

Abstract

Rapidly developing mid-infrared quantum cascade laser (QCL) technology gives easy access to broadly tunable mid-IR laser radiation at a modest cost. Despite several applications of QCL in the industry, its usage for spectroscopic investigation of synthetically relevant organic compounds has been limited. Here we report the application of an external cavity, continuous wave, mid-IR QCL to cryogenic ion vibrational predissociation spectroscopy (CIVP) to analyze a set of large organic molecules, organometallic complexes, and isotopically labeled compounds. The obtained spectra of test molecules are characterized by high signal-to-noise ratio and low FWHM-values, allowing the assignment of two compounds with just a few wavenumbers difference. Data generated by cw-QCL and spectra produced by another standard Nd:YAG DFG system are compared and discussed.

Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy of Aryl Cobinamides in the Gas Phase: How Good Are the Calculations for Vitamin B12 Derivatives?

“…In our experience, harmonic frequencies, computed with BP86-D3 and a triple-ζ basis set, for C–H, N–H, and O–H stretches need scaling by factors very close to unity, e.g. , 0.98 or 0.99 to match experiment. ,, This latter claim can be further supported by the general similarity between the harmonic spectra and the experimental IR spectra for many small molecules and ions, especially in the high-frequency part of the spectrum.…”

“…17 Nitrogen was used as a buffer gas, and the temperature of the trap was kept at 30 K. CIVP spectroscopy was done as previously described. 17,18 Computational Studies. Initial RCbi + structures were obtained with the CREST program (version 2.7.1), 19 which produced up to 300 conformers spanning a range of 6 kcal mol −1 .…”

Probing Electronic Effects in Tridentate Copper(I) Complexes by CIVP Spectroscopy

“…As shown in the past by us 25 and by others, 50−54 IR-active stretching frequencies of N 2 , which is often used as a messenger tag in CIVP spectroscopic investigations, point out that the N 2 can act as a ligand as well as a tag, i.e., the N 2 can be non-innocent. Such behavior can introduce additional problems, when spectra of non-covalently bound organic molecules have to be studied, because an IR-active N 2 tag means that the structure of the investigated ion may be perturbed by the tag in those exceptional cases where the tag itself becomes spectroscopically active.…”

Increasing Complexity in a Conformer Space Step-by-Step: Weighing London Dispersion against Cation−π Interactions

“…Detailed descriptions of the setup, the laser scheme, and experiments for the CIVP measurements have been reported in previous work. − All pyridines, or the corresponding pyridinium salts, were electrosprayed from 5 to 50 μM methanol or methanol-d 4 solutions. The temperature of the heated capillary was held at 170 °C.…”

“…CIVP Spectroscopy in the N−D Stretching Region. Recently, we reported the application of a continuous-wave quantum cascade laser, in combination with CIVP spectroscopy, on selected examples, including isotopically labeled compounds, 34 which gave us, among other advantages, the opportunity to extend the accessible frequency range for our experiment. As the Fermi resonance hindered a completely unambiguous assignment of the gas-phase conformer based on the N−H stretching mode, we decided to effectively "deperturb" the desired chromophore by shifting it out of Fermi resonance to an otherwise empty spectral region by deuterium−hydrogen exchange.…”