Periodic Reporting for period 2 - GASIR (Gas-phase two-dimensional rovibrational infrared spectroscopy of volatile organic compounds)
Reporting period: 2022-11-01 to 2023-10-31
The aim of the project is to develop two-dimensional infrared (2DIR) spectroscopy of gas-phase samples.
2DIR spectroscopy is a well-established and powerful tool used to study structure and dynamics of solid state and liquid samples.
Commonly, three ultrashort pulses, with duration of around or less than 100 femtoseconds, are made to interact with the sample in sequence and the response of the sample is recorded as a function of delays between pulses.
This arrangement allows one study the molecular dynamics involving fundamental molecular vibrations.
2DIR spectroscopy has diverse applications, including energy sciences, biophysics and physical chemistry.
The applications of this technique to gas-phase samples have remained virtually unexplored until now.
2DIR spectroscopy has not been used previously to study gas-phase samples because of insufficient resolution and sensitivity.
This project aims to overcome both of these deficiencies by using optical frequency comb sources.
Moreover, the theory of rotationally-resolved (gas-phase) 2DIR (RR2DIR) spectroscopy is similarly underdeveloped, therefore the project will also develop necessary theoretical and computational tools to interpret the RR2DIR spectra.
The experimental developments will enable high resolution and high sensitivity measurements, while theoretical developments will enable their quantitative interpretation.
Combined, these efforts will develop RR2DIR spectroscopy as a tool for studying complex gas mixtures of polyatomic molecules.
Detection of trace amounts of gases in multi-species mixtures is important for many purposes, ranging from basic science through analysis of complex chemical environments, such as flames, to breath analysis for medical diagnostics.
The project has resulted in theoretical description of 2DIR spectra of gas-phase samples.
This enabled us to discover new polarization conditions - unique to the gas phase - that suppress parts of the molecular response.
These theoretical results were validated by experimental measurements of carbon dioxide 2DIR spectra.
2DIR spectroscopy is a well-established and powerful tool used to study structure and dynamics of solid state and liquid samples.
Commonly, three ultrashort pulses, with duration of around or less than 100 femtoseconds, are made to interact with the sample in sequence and the response of the sample is recorded as a function of delays between pulses.
This arrangement allows one study the molecular dynamics involving fundamental molecular vibrations.
2DIR spectroscopy has diverse applications, including energy sciences, biophysics and physical chemistry.
The applications of this technique to gas-phase samples have remained virtually unexplored until now.
2DIR spectroscopy has not been used previously to study gas-phase samples because of insufficient resolution and sensitivity.
This project aims to overcome both of these deficiencies by using optical frequency comb sources.
Moreover, the theory of rotationally-resolved (gas-phase) 2DIR (RR2DIR) spectroscopy is similarly underdeveloped, therefore the project will also develop necessary theoretical and computational tools to interpret the RR2DIR spectra.
The experimental developments will enable high resolution and high sensitivity measurements, while theoretical developments will enable their quantitative interpretation.
Combined, these efforts will develop RR2DIR spectroscopy as a tool for studying complex gas mixtures of polyatomic molecules.
Detection of trace amounts of gases in multi-species mixtures is important for many purposes, ranging from basic science through analysis of complex chemical environments, such as flames, to breath analysis for medical diagnostics.
The project has resulted in theoretical description of 2DIR spectra of gas-phase samples.
This enabled us to discover new polarization conditions - unique to the gas phase - that suppress parts of the molecular response.
These theoretical results were validated by experimental measurements of carbon dioxide 2DIR spectra.
The project resulted in development of the theory of rotationally-resolved two-dimensional infrared (RR2DIR) spectroscopy.
This theory lays the groundwork for further more detailed investigations of, for example, collisional effects in the spectra or of anharmonic couplings between different vibrational modes.
Two specific features of RR2DIR spectroscopy were investigated more deeply: polarization dependence and waiting time dependence of the molecular response.
The work on polarization dependence resulted in general classification of the molecular response into seven distinct classes.
This enabled derivation of special polarization sequences of incident pulses that turn off specific parts of the 2D spectrum and that greatly simplify the spectrum.
This result will be especially important for detection of complex gas mixtures, such as those found in human breath or in other complex chemical environments, since simplifying the spectrum makes it easier to identify and quantify the concentration of different components.
The waiting time dependence--which is the delay between the second and the third pulse--provides another experimental "knob" that facilitates identification of molecular species.
In particular it was found that at specific times, unique to each molecular species, parts of the spectrum can disappear due to destructive interference.
The project also resulted in a size-dependent model describing rotational dynamics of antenna-equipped argon clusters.
The theoretical results furnish experimental researchers with tools to interpret and analyze their measurements.
These results are complemented with the simulation code, rotsim2d, that was developed as part of the project.
Most importantly, the software enables simulation of actual experimental spectra.
The code can therefore be used as a component of a fitting procedure to retrieve gas concentrations.
Additionally, the software includes visualization tools that help in understanding different aspects of the theory and consequences thereof.
These theoretical results were validated by measurements of 2DIR spectrum of carbon dioxide asymmetric stretch, demonstrating excellent agreement.
The project also resulted in a design of a unique near-infrared RR2DIR spectrometer employing multiple high-power optical frequency combs and a lock-in Fourier-transform spectrometer.
The results of the project were disseminated at numerous conferences in the form of posters and talks.
The results were also presented at several seminar talks.
The theoretical results on 2DIR spectroscopy were published in two peer-reviewed articles.
Moreover, the work on cavity-enhanced transient absorption spectroscopy, which included dynamics of argon clusters, was published in a peer-reviewed article, and the measurements of CO-N2 spectra, which used our Yb:fiber-based MOPA-OPO, were published in a peer-reviewed article.
This theory lays the groundwork for further more detailed investigations of, for example, collisional effects in the spectra or of anharmonic couplings between different vibrational modes.
Two specific features of RR2DIR spectroscopy were investigated more deeply: polarization dependence and waiting time dependence of the molecular response.
The work on polarization dependence resulted in general classification of the molecular response into seven distinct classes.
This enabled derivation of special polarization sequences of incident pulses that turn off specific parts of the 2D spectrum and that greatly simplify the spectrum.
This result will be especially important for detection of complex gas mixtures, such as those found in human breath or in other complex chemical environments, since simplifying the spectrum makes it easier to identify and quantify the concentration of different components.
The waiting time dependence--which is the delay between the second and the third pulse--provides another experimental "knob" that facilitates identification of molecular species.
In particular it was found that at specific times, unique to each molecular species, parts of the spectrum can disappear due to destructive interference.
The project also resulted in a size-dependent model describing rotational dynamics of antenna-equipped argon clusters.
The theoretical results furnish experimental researchers with tools to interpret and analyze their measurements.
These results are complemented with the simulation code, rotsim2d, that was developed as part of the project.
Most importantly, the software enables simulation of actual experimental spectra.
The code can therefore be used as a component of a fitting procedure to retrieve gas concentrations.
Additionally, the software includes visualization tools that help in understanding different aspects of the theory and consequences thereof.
These theoretical results were validated by measurements of 2DIR spectrum of carbon dioxide asymmetric stretch, demonstrating excellent agreement.
The project also resulted in a design of a unique near-infrared RR2DIR spectrometer employing multiple high-power optical frequency combs and a lock-in Fourier-transform spectrometer.
The results of the project were disseminated at numerous conferences in the form of posters and talks.
The results were also presented at several seminar talks.
The theoretical results on 2DIR spectroscopy were published in two peer-reviewed articles.
Moreover, the work on cavity-enhanced transient absorption spectroscopy, which included dynamics of argon clusters, was published in a peer-reviewed article, and the measurements of CO-N2 spectra, which used our Yb:fiber-based MOPA-OPO, were published in a peer-reviewed article.
The theoretical work performed within the project was entirely motivated by the gaps in the existing scientific literature found at the outset of the project.
The derived polarization conditions and predicted waiting time dependence are unique to the gas phase, which up to now has not been explored by 2D spectroscopy.
These novel theoretical results were validated by measurements of carbon dioxide spectra.
Our model of rotational dynamics of argon clusters directly improves on previously used models.
The cavity-enhanced transient absorption spectroscopy measurements are the first of their kind and bridge the gap between gas-phase photoelectron spectroscopy vs liquid-phase pump-probe spectroscopy.
Sensitive and high-resolution 2DIR in the molecular fingerprint region can enable analysis of complex mixtures of polyatomic gases with unprecedented sensitivity and specificity.
These new spectroscopic capabilities would benefit applications in human breath analysis, flame diagnostics, and detection of explosives, as well as fundamental chemical physics studies on problems such as intramolecular vibrational redistribution and collisional dynamics in gases.
For example, unsolved problems in collisional dynamics are holding back interpretation of molecular spectra in gas-phase thermometry, atmospheric research and ultra-accurate measurements of molecular hydrogen transitions.
With a large information density of gas-phase 2DIR spectroscopy, there are likely many unforeseen applications as well.
The work on the high-power near-IR frequency comb source is expected to result in an easy to replicate and highly reliable laser system capable of months-long operation without significant maintenance.
This level of reliability is necessary for the system to serve as the backbone of a cavity-enhanced RR2DIR spectrometer.
It is also important for other applications in spectroscopy and beyond, which are not part of the current project.
In fact, an ultrafast and ultrabroadband optical frequency comb can be used to generate highly coherent and phase stable light from far-infrared/microwave frequencies to the soft x-ray region.
The derived polarization conditions and predicted waiting time dependence are unique to the gas phase, which up to now has not been explored by 2D spectroscopy.
These novel theoretical results were validated by measurements of carbon dioxide spectra.
Our model of rotational dynamics of argon clusters directly improves on previously used models.
The cavity-enhanced transient absorption spectroscopy measurements are the first of their kind and bridge the gap between gas-phase photoelectron spectroscopy vs liquid-phase pump-probe spectroscopy.
Sensitive and high-resolution 2DIR in the molecular fingerprint region can enable analysis of complex mixtures of polyatomic gases with unprecedented sensitivity and specificity.
These new spectroscopic capabilities would benefit applications in human breath analysis, flame diagnostics, and detection of explosives, as well as fundamental chemical physics studies on problems such as intramolecular vibrational redistribution and collisional dynamics in gases.
For example, unsolved problems in collisional dynamics are holding back interpretation of molecular spectra in gas-phase thermometry, atmospheric research and ultra-accurate measurements of molecular hydrogen transitions.
With a large information density of gas-phase 2DIR spectroscopy, there are likely many unforeseen applications as well.
The work on the high-power near-IR frequency comb source is expected to result in an easy to replicate and highly reliable laser system capable of months-long operation without significant maintenance.
This level of reliability is necessary for the system to serve as the backbone of a cavity-enhanced RR2DIR spectrometer.
It is also important for other applications in spectroscopy and beyond, which are not part of the current project.
In fact, an ultrafast and ultrabroadband optical frequency comb can be used to generate highly coherent and phase stable light from far-infrared/microwave frequencies to the soft x-ray region.