About

Marissa Weichman is an Assistant Professor of Chemistry at Princeton University. Her research focuses on using fundamental chemical physics and spectroscopy to probe the detailed behavior of complex chemical systems and develop new methods to steer molecular processes using light. Her lab aims to control molecular processes through strong light-matter interactions, particularly in the emerging field of polariton chemistry, which involves harnessing strong coupling in optical cavities to alter chemical reactions. She is establishing experimental work to validate theories of cavity-modified chemistry by employing ultrafast and high-resolution spectroscopy to track the dynamical trajectories of molecular processes under strong coupling. Additionally, her work includes precision spectroscopy of large molecules, which is crucial for molecular fingerprinting in complex environments and for applications in quantum information science. She develops advanced spectroscopic tools such as cavity-enhanced frequency comb spectroscopy to study astrochemical species and large molecules, establishing new records in molecular size and complexity that can be examined with quantum state resolution. Her research also extends to atmospheric aerosol science, where she advances laboratory spectroscopies to understand how aerosols scatter and absorb light and nucleate cloud droplets, thereby contributing to climate modeling and understanding climate change impacts. Her contributions have been recognized with numerous awards, including the Cottrell Scholar Award, Packard Fellowship, and the Presidential Early Career Award for Scientists and Engineers.

Research topics

• Chemistry
• Atomic physics
• Materials science
• Physics
• Chemical physics

Selected publications

• Supplementary document for Long-wave mid-infrared cavity-enhanced frequency comb spectroscopy of cold, complex molecules - 7727085.pdf

  Figshare · 2026-01-01

  articleOpen accessSenior author

  Supplementary Material containing Table S1

  PublisherDOI

• Electronic Strong Coupling of Gas-Phase Molecular Iodine

  ArXiv.org · 2026-02-09

  articleOpen accessSenior author

  Molecular polaritons, hybrid light-matter states formed from the strong coupling of molecular transitions and discrete photonic modes, are a compelling platform for optical control of chemical reactivity. Despite the origins of the field of polaritonics in atomic gases, strong coupling of molecular gases remains underexplored. The pristine, solvent-free gas-phase environment may prove ideal for gaining mechanistic understanding of molecular behavior under strong light-matter coupling. In this work, we achieve electronic strong coupling of the B-X, $ν_1$ = 0$\rightarrow$32, J = 53$\rightarrow$52 and B-X, $ν_1$ = 0$\rightarrow$34, J = 103$\rightarrow$102 rovibronic transitions of gas-phase iodine (I$_2$) lying near 532.2 nm. We access a range of coupling strengths and detuning conditions with fine control over molecular number density and cavity length stabilization. This effort represents the first demonstration of electronic polaritons in a molecular gas and opens a new platform for polariton photochemistry and photophysics.

  PublisherOA PDF

• Supplementary document for Long-wave mid-infrared cavity-enhanced frequency comb spectroscopy of cold, complex molecules - 7727085.pdf

  Figshare · 2026-01-01

  articleOpen accessSenior author

  Supplementary Material containing Table S1

  PublisherDOI

• Nonlinear signal enhancement of strongly-coupled molecules in pump-probe experiments

  ArXiv.org · 2026-04-06

  articleOpen accessSenior author

  Nonlinear spectroscopy is widely used to study the transient dynamics of molecules under strong light-matter coupling, though it remains unclear to what extent uncoupled intracavity molecules obscure signals from the strongly-coupled species of interest. Pump or probe fields resonant in the strongly-coupled spectral region will preferentially interact with cavity-coupled molecules, but can exhibit severe optical artifacts due to wave interference in the cavity. On the other hand, non-resonant pump or probe fields having wavelengths at which the cavity mirrors are highly transmissive propagate as traveling waves along the cavity axis, interacting with both coupled and uncoupled intracavity molecules. Here, we quantify the contributions of signals from strongly-coupled and uncoupled populations in simulated experiments with different resonant and non-resonant pump-probe configurations. We find that while resonant schemes maximize selectivity for the signals of strongly-coupled molecules, non-resonant schemes retain surprisingly high sensitivity to these signals while remaining less susceptible to optical artifacts.

  PublisherOA PDF

• Tracking water vapor homogeneous nucleation and droplet growth with spectroscopy and holography in a free expansion cloud chamber

  ArXiv.org · 2026-05-12

  articleOpen accessSenior author

  We use a newly commissioned rapid expansion aerosol chamber (REACh) facility to study the homogeneous nucleation of water vapor to form liquid droplets. We perform high-speed measurements to track the partitioning of water into vapor and droplets throughout the expansion process, including tunable diode laser absorption spectroscopy (TDLAS) to access the vapor concentration and in-line holography to track the size and concentration of nucleating droplets. We retrieve the peak saturation ratio achieved in each expansion from the TDLAS measurements in combination with adjusted thermocouple temperature readout. We monitor the number of nucleated droplets and their subsequent growth as a function of saturation ratio, and observe the onset of homogeneous nucleation of water vapor occurring at a threshold saturation ratio near $S=5$, in agreement with prior literature and classical nucleation theory. The trends we observe in average diameter and droplet concentration suggest that warm air pockets near the chamber walls inhomogeneously mix with cold air at the center of the chamber following expansion. Active forced mixing with fans yields more spatially uniform temperature readings across the chamber, but also significantly broadens the droplet size distribution. Our results demonstrate the capability of TDLAS and holography techniques to track both water vapor and liquid water in the high saturation ratio environments necessary for the homogeneous nucleation of droplets. Our findings also reveal that droplet nucleation and growth dynamics are highly sensitive to turbulence.

  PublisherOA PDF

• Electronic Strong Coupling of Gas-Phase Molecular Iodine

  Open MIND · 2026-02-09

  preprintSenior author

  Molecular polaritons, hybrid light-matter states formed from the strong coupling of molecular transitions and discrete photonic modes, are a compelling platform for optical control of chemical reactivity. Despite the origins of the field of polaritonics in atomic gases, strong coupling of molecular gases remains underexplored. The pristine, solvent-free gas-phase environment may prove ideal for gaining mechanistic understanding of molecular behavior under strong light-matter coupling. In this work, we achieve electronic strong coupling of the B-X, $ν_1$ = 0$\rightarrow$32, J = 53$\rightarrow$52 and B-X, $ν_1$ = 0$\rightarrow$34, J = 103$\rightarrow$102 rovibronic transitions of gas-phase iodine (I$_2$) lying near 532.2 nm. We access a range of coupling strengths and detuning conditions with fine control over molecular number density and cavity length stabilization. This effort represents the first demonstration of electronic polaritons in a molecular gas and opens a new platform for polariton photochemistry and photophysics.

  DOI

• Long-wave mid-infrared cavity-enhanced frequency comb spectroscopy of cold, complex molecules

  Optics Express · 2026-02-06

  articleOpen accessSenior author

  We report the development of an instrument for cavity-enhanced absorption spectroscopy of the fundamental rovibrational transitions of molecules in the long-wave mid-infrared (LWIR) region from 6500 to 10000 nm. Our setup combines an LWIR frequency comb, a high-finesse optical enhancement cavity, a cryogenic buffer gas cooling cell, and a Fourier transform interferometer to obtain broadband, high-resolution, and high-sensitivity molecular absorption spectra. Here, we showcase the capabilities of this setup by presenting the gas-phase LWIR spectra of the ν 6 band of ethane and the ν 10 band of the gauche conformer of ethanol near 7200 nm under both room temperature and cryogenic conditions.

  PublisherDOI

• Direct Readout of Excited-State Lifetimes in Chlorin Chromophores under Electronic Strong Coupling

  Journal of the American Chemical Society · 2026-02-27

  articleOpen accessSenior authorCorresponding

  The mechanisms governing molecular photophysics under electronic strong coupling (ESC) remain elusive to date. Here, we use ultrafast pump–probe spectroscopy to study the excited-state relaxation dynamics of chlorin e6 trimethyl ester (Ce6T) under strong coupling of its transition from the electronic ground state to the Qy band. Ce6T is a compelling testbed with which to address open questions about excited-state lifetimes under ESC given prior reports of cavity-altered behavior in chlorins. We use dichroic Fabry-Pérot cavities to provide a transparent spectral window in which we can directly track the excited-state population following the optical pumping of either the strongly-coupled Qy band or the higher-lying B band. This scheme circumvents many of the optical artifacts inherent in ultrafast cavity measurements and allows for facile comparison of strongly-coupled measurements with extracavity controls. We observe no significant changes in excited-state lifetimes for any optical pumping schemes or cavity-coupling conditions considered herein. These results suggest that Ce6T exhibits identical photophysics under ESC and in free space, presenting a new data point for benchmarking emerging theories for cavity photochemistry.

  PublisherDOI

• Tracking water vapor homogeneous nucleation and droplet growth with spectroscopy and holography in a free expansion cloud chamber

  arXiv (Cornell University) · 2026-05-12

  preprintOpen accessSenior author

  We use a newly commissioned rapid expansion aerosol chamber (REACh) facility to study the homogeneous nucleation of water vapor to form liquid droplets. We perform high-speed measurements to track the partitioning of water into vapor and droplets throughout the expansion process, including tunable diode laser absorption spectroscopy (TDLAS) to access the vapor concentration and in-line holography to track the size and concentration of nucleating droplets. We retrieve the peak saturation ratio achieved in each expansion from the TDLAS measurements in combination with adjusted thermocouple temperature readout. We monitor the number of nucleated droplets and their subsequent growth as a function of saturation ratio, and observe the onset of homogeneous nucleation of water vapor occurring at a threshold saturation ratio near $S=5$, in agreement with prior literature and classical nucleation theory. The trends we observe in average diameter and droplet concentration suggest that warm air pockets near the chamber walls inhomogeneously mix with cold air at the center of the chamber following expansion. Active forced mixing with fans yields more spatially uniform temperature readings across the chamber, but also significantly broadens the droplet size distribution. Our results demonstrate the capability of TDLAS and holography techniques to track both water vapor and liquid water in the high saturation ratio environments necessary for the homogeneous nucleation of droplets. Our findings also reveal that droplet nucleation and growth dynamics are highly sensitive to turbulence.

  PublisherDOI

• Nonlinear signal enhancement of strongly-coupled molecules in pump-probe experiments

  arXiv (Cornell University) · 2026-04-06

  preprintOpen accessSenior author

  Nonlinear spectroscopy is widely used to study the transient dynamics of molecules under strong light-matter coupling, though it remains unclear to what extent uncoupled intracavity molecules obscure signals from the strongly-coupled species of interest. Pump or probe fields resonant in the strongly-coupled spectral region will preferentially interact with cavity-coupled molecules, but can exhibit severe optical artifacts due to wave interference in the cavity. On the other hand, non-resonant pump or probe fields having wavelengths at which the cavity mirrors are highly transmissive propagate as traveling waves along the cavity axis, interacting with both coupled and uncoupled intracavity molecules. Here, we quantify the contributions of signals from strongly-coupled and uncoupled populations in simulated experiments with different resonant and non-resonant pump-probe configurations. We find that while resonant schemes maximize selectivity for the signals of strongly-coupled molecules, non-resonant schemes retain surprisingly high sensitivity to these signals while remaining less susceptible to optical artifacts.

  PublisherDOI

Recent grants

• CAREER: Gas-Phase Molecular Polaritons: A New Platform for Chemistry under Strong Light-Matter Coupling

  NSF · $650k · 2023–2028

Frequent coauthors

• Daniel M. Neumark

  University of California, Berkeley

  93 shared

• P. Bryan Changala

  Center for Astrophysics Harvard & Smithsonian

  51 shared

• Jongjin B. Kim

  SLAC National Accelerator Laboratory

  29 shared

• Jessalyn A. DeVine

  University of Göttingen

  29 shared

• Jun Ye

  University of Colorado Boulder

  27 shared

• Mark Babin

  27 shared

• Kana Iwakuni

  University of Electro-Communications

  16 shared

• Kevin Lee

  USA Mitchell Cancer Institute

  15 shared

Labs

• Weichman LabPI

Education

• Ph.D., Chemistry

  University of California Berkeley

  2017

• B.S., Chemistry

  California Institute of Technology

  2012

Awards & honors

• Cottrell Scholar Award 2025
• Presidential Early Career Award for Scientists and Engineers…
• Packard Fellowship for Science and Engineering 2023
• NSF CAREER 2023
• DOE Early Career Award 2022