Microwave spectral taxonomy: A semi-automated combination of chirped-pulse and cavity Fourier-transform microwave spectroscopy

Abstract

Because of its structural specificity, rotational spectroscopy has great potential as an analytical tool for characterizing the chemical composition of complex gas mixtures. However, disentangling the individual molecular constituents of a rotational spectrum, especially if many of the lines are entirely new or unknown, remains challenging. In this paper, we describe an empirical approach that combines the complementary strengths of two techniques, broadband chirped-pulse Fourier transform microwave spectroscopy and narrowband cavity Fourier transform microwave spectroscopy, to characterize and assign lines. This procedure, called microwave spectral taxonomy, involves acquiring a broadband rotational spectrum of a rich mixture, categorizing individual lines based on their relative intensities under series of assays, and finally, linking rotational transitions of individual chemical compounds within each category using double resonance techniques. The power of this procedure is demonstrated for two test cases: a stable molecule with a rich spectrum, 3,4-difluorobenzaldehyde, and products formed in an electrical discharge through a dilute mixture of C2H2 and CS2, in which spectral taxonomy has enabled the identification of propynethial, HC(S)CCH.

Carbon–sulfur chains: A high‐resolution infrared and quantum‐chemical study of C3S and SC7S

“…Based on the ground state rotational constant of the ν 3 state (located at about 722 cm −1 above ground, Table ) very recently characterized with Fourier transform microwave spectroscopy and the CCSD(T) anharmonic force field calculations providing an anharmonicity constant of cm −1 , the spectrum shown in Figure was also checked for the presence of the hot band. Indeed, a weak series comprising a total of 37 transitions could be assigned to this new hot band.…”

“…[6, 51, 53, 54]. The millimeter wave data of the state were taken from Tang and Saito and the microwave data for from Crabtree et al In addition, the high‐resolution infrared data from Takano et al were used for the ν 1 fundamental and the hot band. As for the parent species, the v = 0 data of the 34 S isotopolog were used as summarized in the CDMS (entry 070502).…”

“…However, in the past millimeter wave studies were devoted to the study of vibrational satellites up to (Ref. ) and, also very recently, vibrational satellites from the energetically lowest stretching mode ν 3 (and several of its overtones) and from the first overtone of ν 4 were observed . As a result, good descriptions of lower states that might be involved in hot bands are already available to support further spectroscopic analyses in the future.…”

“… and references therein), as well as microwave spectroscopy (Refs. and references therein). Besides the neutral species, negatively charged variants were observed using photoelectron and matrix isolation spectroscopy (Refs.…”

The Hydrogen Bond and Beyond: Perspectives for Rotational Investigations of Non‐Covalent Interactions

“…Appreciation of molecular recognition models, the role of molecular flexibility, and the balance of NCIs, including cooperative and competitive effects, will require the systematic examination of larger, more realistic molecular systems. The progress toward detailed structural characterization of large clusters will come from a combination of advances in microwave instrumentation and double‐resonance techniques, automated computer analysis, and molecular modelization . In particular, the synergy of broadband rotational spectroscopy and supporting quantum mechanical predictions will be crucial for future analyses.…”