This presentation describes the application of a miniature millimeter-wave rotational spectrometer to the detection of laser-ablation products. The laboratory experiments we present are forerunners to possible future field- or space deployments. We focus on NaCl and KCl salts, which are interesting targets at the icy moons of the outer solar system. The laser-coupled spectrometer incorporates a collisional-cooling, pulsed carrier gas beam. We leverage the small size of the spectrometer cavity to probe the ablation product signal along the beam length. We find that the volatilized species are widely dispersed in the carrier-gas. Additionally, we present centimeter-wave rotational and mass spectroscopic measurements to help characterize the laser ablation process.

Absorption spectroscopy typically recovers the average thermodynamic properties along a laser path. However, broadband laser sources, including the dual frequency comb spectrometer, measure many absorption features which provide different temperature information about the path nonuniformity. We have developed a two-step approach to extract a nonuniform temperature distribution from a broadband absorption spectrum spanning hundreds of absorption features. We demonstrate how this approach resolves the path nonuniformity in a tube furnace as predicted by natural convection theory.

The molecular diversity of cold interstellar medium has been recently enriched with the detection of molecular anions: C₄H⁻, C₆H⁻, C₈H⁻, C₃N⁻, C₅N⁻ and CN⁻. Although by far less abundant than neutrals, anions could play a significant role in the chemistry of molecular cloudsA. Van Orden, R.J. Saykally, Chem. Rev. 98 (1998) 2313-2358^,W. Weltner Jr, R.J. Van Zee, Chem. Rev. 89 (1989) 1713−1747 With the exception of C_5N^-, whose identification in space was based on high−level ab initio calculationsJ. Cernicharo et al. The Astrophysical Journal 688, no 22008: L83 86 the astronomical detection of these anions was made possible thanks to the laboratory characterization of their rotational spectra. Our ultimate goal is to characterize the anionic carbon chains C_x^- (x = 3, 4, 5,…) through their electronic spectra in order to explain the absorption features already observed one century ago in some diffuse interstellar clouds illuminated by reddened stars. We will represent our new instrument based on a planar de Laval supersonic plasma source coupled to Incoherent Broadband Cavity−Enhanced Absorption Spectroscopy (IBB−CEAS) in conjunction with a high−resolution Fourier transform spectrometer for the detection. Preliminary results obtained on neutral species (O_2, CH_4, C_2H_2 W. Weltner Jr, R.J. Van Zee, Chem. Rev. 89 (1989) 1713-1747.J. Cernicharo et al. The Astrophysical Journal 688, no 22008: L83 86,

A new technique that uses non-parametric four wave mixing for generating high resolution coherent 3D (HRC3D) spectra has been developed. This technique produces spectra with rotational peaks that are distributed in 3D space. A new approach to scanning has been developed where orthogonal 2D slices are combined to create a 3D rotational pattern. The 3D pattern can then be used to rapidly calculate rotational constants without the need for other forms of spectroscopy.

High resolution coherent multidimensional spectroscopy automatically sorts peaks sequentially by rotational quantum number. This presentation describes the use of the method of combination differences to determine both quantum numbers and Dunham coefficients from peaks in coherent multidimensional spectra.

We have developed a new apparatus that combines cw-cavity ringdown spectroscopy with a pulsed Laval flow (UF-CRDS)N. Suas-David, S. Thawoos, and A. G. Suits, The Journal of Chemical Physics 151 (2019) 244202 This is related to the CRESU technique developed in France to study reaction kinetics at low temperaturesB. Rowe et al., The Journal of Chemical Physics 80 (1984) 4915. Cavity ringdown spectroscopy (CRDS) is a highly sensitive absorption technique relying on the decay of light between two high reflectivity mirrors of a cavity. For time-independent absorbing samples, the enhanced rate of power loss compared to the empty cavity leads to faster exponential decays. When the concentration of the absorbing species changes on the time scale of the empty cavity ring-down time, non-exponential decays result, for which the instantaneous decay rate in excess of the empty cavity reference case provides a time-resolved measure of the sample absorbance. The long hydrodynamic time of the flow provides uniform temperature and pressure conditions well-matched to kinetic ring-down measurements in the time regime from 10-300 microseconds. This simultaneous kinetics and ring-down (SKaR) techniqueS. S. Brown, A. Ravishankara, and H. Stark, The Journal of Physical Chemistry A 104 (2000) 7044.s here coupled with a uniform flow for the first time. We will be presenting rate constants measured for reactions of CN(v=1) with O₂ at a range of temperatures from 70- 23 K obtained with this approach.

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Footnotes:

N. Suas-David, S. Thawoos, and A. G. Suits, The Journal of Chemical Physics 151 (2019) 244202. B. Rowe et al., The Journal of Chemical Physics 80 (1984) 4915.. S. S. Brown, A. Ravishankara, and H. Stark, The Journal of Physical Chemistry A 104 (2000) 7044.i

The high amount of reactive species participating in the chemistry in the Earth^′s upper atmosphere, interstellar medium, or combustion processes motivates laboratory experimentalists to develop efficient methods for the molecular in situ generations to characterize these species spectroscopically. In the present contribution, we propose a new approach based on the laser ablation of solid organic compounds. A proof-of-concept experiment is performed using diaminomaleonitrile and uridine as prototypical precursors. Once formed in the throat of our laser ablation source, the products are entrained in the carrier gas, stabilized in the cold environment of the supersonic expansion, and are monitored by high-resolution chirped pulse Fourier transform microwave spectroscopy. We experimentally demonstrate a simultaneous formation of an impressive number and variety of species, both known and unknown. With these inspiring achievements in hands, we extend the boundaries for the molecular in situ generations beyond traditional techniques such as electric discharge and pyrolysis.

At the 74th ISMS, our group showed that it is possible to detect microwave radiation in a CP-FTMW experiment that does not copropagate with the incidence of radiation. In that talk, it was shown that this could be achieved with the broadcast antenna by the implementation of a circulator, switch, and low noise amplifier in order to also detect off of the same antenna. Coincidentally, the circulator that was utilized attenuated the input power below a level where this detection would be advantageous to the overall signal-to-noise ratio (SNR) of the collected free induction decays (FIDs). However, this discovery provided both the preliminary data and the impetus for a new hypothesis to be tested: Could FIDs be detected at other points not in the direct linear path of the microwaves? To address this, we utilized our new microwave three-wave mixing (M3WM) instrument based upon the four-antennae design of Pate in order to utilize the orthogonality of the setup for the purposes of CP-FTMW FID collection. The design of the new four-antennae MAD-CP-FTMW at Missouri S&T will be presented along with the exciting results of detection in traditional, 180 degree, and quadrature angles. Additional testing, done to mitigate the concern of reflection voiced in the original presentation, will also be discussed. Any post-processing of data needed in order to enhance SNR using these methods will also be discussed.

We discuss current challenges in the preparation of thin film samples for extreme ultraviolet (XUV) spectroscopy, and offer alternative methods which now enable this spectroscopy to be performed on a wide variety of previously inaccessible compounds. We explored the production, characterization, and use of polymer thin films as highly XUV transmissive sample supports, finding that such thin films could be made via a “slip-coating” technique in which polymer solution is deposited from the shearing meniscus between parallel sliding glass plates. Films made from polystyrene or polyvinyl chloride are thin (10²-10³ nm), homogeneously flat, smooth, and transmit more XUV light than do silicon nitride windows. The analytes of interest are directly cast upon the polymer surface, or codeposited from a common solution. In demonstration of the suitability of these methods towards XUV spectroscopy, we prepared samples of eight different first-row transition metal complexes and report their respective M-edge XANES spectra in the range of 40-90 eV. We additionally report the excited state difference spectrum of Fe(bpy)₃Cl₂ at 1.5 ps after visible excitation.

We will present an instrument developed in house able to produce cold molecular ions and ionic van der Waals complexes. The aim of this instrument is to study such species by high-resolution photodissociation spectroscopy. Its main components are (i) a pulsed supersonic expansion plasma source, to produce the desired species at relatively low rotational temperature (50-70K), (ii) a time of flight mass spectrometer which includes a single unit able to perform acceleration, bunching and gatingC. Dedman, Review of Scientific Instruments 72 (2001) 2915-2922 and (iii) a photodissociation laser followed by a second mass selection of the fragmented ion. We will be presenting the first results obtained with this apparatus, (i)the first mass spectra of cationic and anionic species, formed from different gas mixtures and (ii) the first photodissociation spectra of the rovibronic overtones of N₂O⁺ using a dye laser. Finally, future improvements, in terms of clusters production, spectral resolution and sensitivity will be discussed.

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Footnotes:

C. Dedman, Review of Scientific Instruments 72 (2001) 2915-2922,

Super-resolution spectroscopy is essential for the understanding of molecular fine structures, excited state population, distribution function of given energy states, and remote sensing applications. We addressed several key measures for achieving high performances of sprectal resolution and absorbance precision in a mid-infrared modulated laser spectrometer with a distributed feedback interband cascade laser, including linearization of laser scanning, suppression or deduction of optical fringe interferences, and internal calibration for baseline problems and nonlinear response of the photodiode used in the system. The performances of our modified spectrometer were verified with the spectral resolution in the order of 10-6 cm-1 (~hundreds kHz) and absorbance uncertainty in the order of 10-3. We provided a detailed error analysis with the uncertainty model of GUM, i.e. Guide to the expression of uncertainty in measurement. Further, we ensured the traceability of the spectrometer by linking a practical calibration reference standard. We measured the fundamental absorption of several organic molecules, e.g. dimethyl sulfide (CH3)2S), methyl mercaptan (CH3SH) with our modified spectrometer. The recorded spectra were demonstrated to be similar to that in the Pacific Northwest National Laboratory (PNNL) database. These data have been used in our remote sensing applications.