It has been observed that with the advances being driven by the wireless communications industry, the microwave components for submillimeter wave spectrometers and sensors will become almost "free". Moreover, these electronic components will require little power. However, neither of these attributes applies to the vacuum requirements for high-resolution rotational spectroscopy. We will report on the design, construction, and operation of a simple spectroscopic cell that overcomes these problems.

3-D printing is a new technology whose applications are only beginning to be explored. In this report, we describe the application of 3-D printing to the facile design and construction of supersonic nozzles. The efficacy of a variety of designs is assessed by examining rotational spectra OCS and Ar-OCS using a Fourier transform microwave spectrometer with tandem cavity and chirped-pulse capabilities. This work focuses primarily on the use of slit nozzles but other designs have been tested as well. New nozzles can be created for $0.50 or less each, and the ease and low cost should facilitate the optimization of nozzle performance (e.g., jet temperature or cluster size distribution) for the needs of any particular experiment.

The extension of radio-frequency CMOS circuitry into millimeter wavelengths promises the extension of spectroscopic techniques in compact, power efficient systems. We are now exploring the use of CMOS millimeter devices for low-mass, low-power instrumentation capable of remote or in-situ detection of gas composition during space missions. This effort focuses on the development of a semi-confocal Fabry-Perot cavity with mm-wavelength CMOS transmitter and receiver attached directly to a cavity coupler. Placement of the devices within the cavity structure bypasses problems encountered with signal injection and extraction in traditional cavity designs and simultaneously takes full advantage of the miniaturized form of the CMOS hardware. The presentation will provide an overview of the project and details of the accomplishments thus far, including the development and testing of a pulse modulated 83-98 GHz transmitter.

Chriped-pulse Fourier Transform Microwave (CP-FTMW) technology has transformed traditional microwave spectroscopy into a rapid-acquisition, broadband spectral technique. The CP-FT technique has recently been expanded to the millimeter-wave region, but this approach requires costly equipment that is not readily available in most spectroscopy labs. To overcome this challenge, a new experiment has been designed that combines the broadband aspects of CP-FTMW with the high sensitivity of (sub) millimeter absorption spectroscopy. Using the arbitrary waveform generator from a CP-FTMW experiment, and the frequency multipliers and hot electron bolometer detector from a (sub) millimeter wave experiment, we have designed and benchmarked a highly sensitive spectrometer that offers broad spectral coverage and rapid spectral acquisition speeds. This technique is comparable in performance to other rapid-acquisition techniques currently used in the (sub) millimeter range, but offers more sensitivity after averaging. The design of this instrument and the benchmarking results will be presented.

Microwave-millimeter double resonance spectroscopy has been commonly applied by driving absorption with the millimeter light and then probing the resonance using a Fourier Transform Microwave (FTMW) spectrometer. We will present data from an inverse scheme, in which millimeter light is used to probe a transition whose intensity is modulated by the application of microwave radiation. This detection scheme is effective in aiding the assignment of millimeter-wave transitions by revealing which energy levels are associated with particular spectral lines. To increase the speed of this detection technique, we incorporated an arbitrary waveform generator into the microwave source to rapidly sweep the microwave radiation through a broad frequency range. We will discuss this approach as applied to pulsed valve experiments and in combination with a laser-induced chemistry experiment. Potential applications to other experimental designs will also be discussed.

We report double-resonance experiments using broadband chirped-pulse Fourier transform microwave spectroscopy that facilitate spectral assignment and yield information about weak transitions with high resolution and sensitivity. Using the diastereomers menthone and isomenthone as examples, we investigate both the amplitude and the phase dependence of the free-induction decay of the microwave signal transition from pumping a radio frequency transition sharing a common level. l0pt Figure We observe a strong phase change when scanning the radio frequency through molecular resonance. The direction of the phase change depends on the energy level arrangement, i.e., if it is progressive or regressive. The experimental results can be simulated using the density-matrix formalism using the three-level Bloch equations and are best described with the AC Stark effect within the dressed-state picture, resulting in an Autler-Townes splitting. The characteristic phase inversion allows for a) the precise frequency determination of the typically weak radio frequency transitions exploiting the high sensitivity of the connected strong microwave signal transition and b) definitive information about the connectivity of the energy levels involved, i.e., progressive vs. regressive arrangements.

Microwave three-wave mixing experiments have been shown to provide a novel and sensitive way to generate and measure enantiomer-specific molecular signatures. The handedness of the sample can be obtained from the phase of the molecular free induction decay whereas the enantiomeric excess can be determined by the amplitude of the chiral signal. After the introduction of this technique by Patterson et al.Patterson, D.; Schnell, M.; Doyle, J. M. Enantiomer-Specific Detection of Chiral Molecules via Microwave Spectroscopy. Nature 2013, 497, 475–477.emarkable improvements have been realized and experimental strategies for both absolute phase determination and enantiomeric excess have been presented.Patterson, D.; Doyle, J. M. Sensitive Chiral Analysis via Microwave Three-Wave Mixing. Phys. Rev. Lett. 2013, 111, 023008.^, Shubert, V. A.; Schmitz, D.; Patterson, D.; Doyle, J. M.; Schnell, M. Identifying Enantiomers in Mixtures of Chiral Molecules with Broadband Microwave Spectroscopy. Angew. Chem. Int. Ed. 2014, 53, 1152–1155.TLobsiger, S.; Perez, C.; Evangelisti, L.; Lehmann, K. K.; Pate, B. H. Molecular Structure and Chirality Detection by Fourier Transform Microwave Spectroscopy. J. Phys. Chem. Lett. 2014, 6, 196–200.H

A combination of chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy and cavity Fourier transform microwave (c-FTMW) spectroscopy has been used to analyze the spectra of 3,4-difluorobenzaldehyde and two distinct fluoropyridine – carbon dioxide complexes. In all cases, the 8 – 18 GHz CP-FTMW spectrum was measured, and the most intense transitions were chosen for further analysis. The intensities of the identified transitions were measured at multiple polarization powers using the c-FTMW spectrometer. Subsequently, a series of double-resonance experiments were performed on these transitions, again using the c-FTMW spectrometer, in order to discover which transitions shared a common quantum state. Following the double-resonance experiments, the assignments of the spectra were trivial. The results of the spectroscopic analysis, as well as the semi-automated method, will be presented.

Plasmas used in the semiconductor manufacturing industry are of a similar nature to the environments often created for submillimeter spectroscopic study of astrophysical species. At the low operating pressures of these plasmas, submillimeter absorption spectroscopy is a method capable of measuring the abundances and temperatures of molecules, radicals, and ions without disturbing any of the properties of the plasma. These measurements provide details and insight into the interactions and reactions occurring within the plasma and their implications for semiconductor manufacturing processes. A continuous wave, 500 to 750 GHz, absorption spectrometer was designed and used to make measurements of species in semiconductor processing plasmas. Comparisons with expectations from theoretical plasma models provide a basis for validating and improving these models, which is a complex and difficult science itself. Furthermore, these comparisons are an evaluation for the use of submillimeter spectroscopy as a diagnostic tool in manufacturing processes.

Recent developments in instrumentation have made it possible to collect broadband rotational spectra far faster than those spectra can be assigned. As such, we have been working to develop automated assignment algorithms so that the analysis can catch up with the data acquisition. The AUTOFIT programSeifert, N.A., Finneran, I.A., Perez, C., Zaleski, D.P., Neill, J.L., Steber, A.L., Suenram, R.D., Lesarri, A., Shipman, S.T., Pate, B.H., J. Mol. Spec., in pressas made strides in this direction, but it is still quite slow on spectra with high line densities, such as those collected near room temperature. Given that the AUTOFIT algorithm is highly parallelizable, we have used Amazon's EC2 webservice to run a modified version of AUTOFIT simultaneously across a large number of cores, allowing us to obtain results in a fraction of the time normally required by a typical desktop computer. In this talk, we will describe how AUTOFIT was modified to run on EC2 and present some benchmark results.

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Footnotes:

Seifert, N.A., Finneran, I.A., Perez, C., Zaleski, D.P., Neill, J.L., Steber, A.L., Suenram, R.D., Lesarri, A., Shipman, S.T., Pate, B.H., J. Mol. Spec., in pressh