About

Carter Johnson is a visual artist whose diverse technological practice is unified by a political approach to media-making that addresses technology and daily life. His current projects address the convergence of being, politics, and economy in the performance of identity. They center on a suspicion that a sentient intelligence already exists within his home network, and is currently attempting to make first-contact. Employing video projection, algorithmic audiovisual generation, performance, social media, writing, drawing, and animation, his practice articulates an approach to identity and philosophy as a way to the particularity in neo-liberal systems of being – thus connecting the exploitation of bodies and the exploitation of the environment – as they coincide with the digital. Formerly a practicing architect, he has studied literature at Columbia University, architecture at MIT, and art at Hunter College, where he received his second BA and MFA. Carter Johnson currently lives and works in New York City.

Research topics

• Organic chemistry
• Chemistry
• Photochemistry
• Combinatorial chemistry
• Physical chemistry
• Chemical physics
• Physics
• Computational chemistry

Selected publications

• Sequential Ag doping of Au25- atomically precise nanoclusters induces alternating positive and negative shifts of HOMO-LUMO gap

  ChemRxiv · 2025-04-21

  preprintOpen accessSenior author

  Au25 is the most studied atomically precise metal nanocluster and is frequently used to explore the effects of doping on nanocluster performance in a range of applications. A quantitative accounting of the impact of dopants on its electronic structure remains elusive due to the inability to isolate clusters with exact numbers of dopants and the low resolution of experimental techniques used to probe electronic structure. We present high-resolution UV-vis spectra of Au(25-n)Agn(SC6H13)18- (n=0-6) exactly purified by mass spectrometry. These spectra feature substructure in the transitions among the frontier orbitals that reveal their shifts upon doping. Ag-doping blue shifts most spectral features, in accordance with theoretical predictions and observations, but the HOMO-LUMO gap shows an alternating pattern of red and blue shifts with increasing Ag substitution. We interpret these spectral shifts using the superatomic (jellium) model as resulting from perturbations to specific superatomic orbitals with nodes or nodal planes oriented with respect to the Ag dopant sites. These results show an unanticipated quantized doping effect that can be rationalized using accepted intuitive models and serve as clear quantitative tests for ongoing efforts to improve quantum chemical treatments of doped nanoclusters.

  PublisherOA PDFDOI

• Structural Impacts of the Addition of Succinic Acid to Cationic Ammonium Bisulfate Clusters

  ChemRxiv · 2025-06-18

  preprintOpen accessSenior author

  The process by which atmospheric trace vapors cluster and grow into climatically-relevant sizes is called new particle formation (NPF). While sulfuric acid and ammonia are the most abundant acid and base in the atmosphere, these two vapors alone cannot adequately explain observed NPF rates, and organic acids have been studied as a third vapor that could stabilize new particles or drive NPF on their own. We used infrared spectroscopy and mass spectrometry to characterize the structure of clusters composed of succinic acid (SuA), ammonia and sulfuric acid. We show that the structures of ammonium-bisulfate clusters are largely retained upon binding of up to two SuA molecules. Computed structures show significant COOH-COOH hydrogen bonding. These observations suggest that, even at these small sizes, these clusters feature incipient inorganic-organic phase separation. We also find that, despite the fact that the inorganic portion of these clusters feature more hydrogen bond donors than acceptors, there are few free carboxylic acid OH groups, suggesting that the cluster surface is relatively non-polar and depleted in binding sites for further vapors. Increasing SuA content is correlated to spectral broadening, suggesting that organic-enriched new particles are likely to be more fluxional than inorganic ones.

  PublisherOA PDFDOI

• Structural Impacts of the Addition of Succinic Acid to Cationic Ammonium Bisulfate Clusters

  The Journal of Physical Chemistry A · 2025-08-15

  articleSenior authorCorresponding

  The process by which atmospheric trace vapors cluster and grow into climatically relevant sizes is called new particle formation (NPF). While sulfuric acid and ammonia are the most abundant acid and base in the atmosphere, these two vapors alone cannot adequately explain observed NPF rates, and organic acids have been studied as a third vapor that could stabilize new particles or drive NPF on their own. We used infrared spectroscopy and mass spectrometry to characterize the structure of clusters composed of succinic acid (SuA), ammonia and sulfuric acid. We show that the structures of ammonium-bisulfate clusters are largely retained upon binding of up to two SuA molecules. Computed structures show significant COOH-COOH hydrogen bonding. These observations suggest that, even at these small sizes, these clusters feature incipient inorganic-organic phase separation. We also find that, despite the fact that the inorganic portion of these clusters feature more hydrogen bond donors than acceptors, there are few free carboxylic acid OH groups, suggesting that the cluster surface is relatively nonpolar and depleted in binding sites for further vapors. Increasing SuA content is correlated to spectral broadening, suggesting that organic-enriched new particles are likely to be more fluxional than inorganic ones.

  PublisherDOI

• Photochemical Mechanisms in Atmospherically-Relevant Iodine Oxide Clusters

  ChemRxiv · 2024-05-08

  preprintOpen accessSenior author

  Atmospheric new particle formation (NPF) events can be driven by iodine oxides or oxoacids via both neutral and ionic mechanisms. Photolysis of new particles likely plays a significant role in their growth mechanisms, but their spectra and their photolysis mechanisms remain difficult to characterize. We recorded UV photodissociation spectra of (I2O5)0-3(IO3-) clusters, observing O atom, I2O4, and (I2O5)1,2 fragments in the atmospherically-relevant range 300-340 nm. With increasing cluster size, absorption red shifts and generally increases in intensity, suggesting particles photolyze more frequently as they grow. Estimates of the rates indicate that even relatively small clusters are likely to undergo photolysis in ambient conditions. Vibrational spectra identify the covalent moiety I3O8- as the likely chromophore, not IO3-. The (I2O5)-loss pathway competes with particle growth while the slower O loss pathway likely produces triplet O + triplet cluster products that could drive subsequent intra-particle chemistry, particularly with co-adsorbed organic or amine species.

  PublisherOA PDFDOI

• Laboratory mass spectrometry of intact atmospherically-relevant particles

  Journal of Aerosol Science · 2024-12-16 · 1 citations

  articleSenior authorCorresponding
  PublisherDOI

• Resonance Effects from Substituents on L-Type Ligands Mediate Synthetic Control of Gold Nanocluster Frontier Orbital Energies

  ChemRxiv · 2024-05-06

  preprintOpen accessSenior author

  The ligands of metal nanoclusters exert a profound effect on their properties and reactivity, but a systematic explanation for these impacts comparable to that of mononuclear coordination complexes does not currently exist. We show that quantitative control of frontier orbital energies of prototypical Au-PPh3 nanoclusters is driven by resonance effects reaching from the exterior of the ligand shell to the HOMO and LUMO orbitals that are nominally located in the cluster core. Hammett studies of Au-PPh3 ligands with para- and meta- methyl and methoxy groups indicate that electronic resonance effects dominate electrostatic effects, but do not specify whether resonance effects stop at the Au-P bond or extend into the cluster core. Quantum chemical calculations show no significant trend in charge on the Au atoms, but do show a pattern of alternating shortened and lengthened bonds that includes the Au-P bond, consistent with resonance effects spanning the full cluster. Computed orbitals show a substantial contribution from atomic orbitals of the ligand substituent to the cluster-core-based HOMO orbital for the para- case, mediated by phenyl ring and phosphorous orbitals. These results suggest that a resonance picture must exist to rationalize ligand effects in nanoclusters and, potentially, nanoparticles, even in the ground state. These resonance effects can be used to engineer cluster properties and reactivity and modulate energy and charge transfer in and out of nanoclusters.

  PublisherOA PDFDOI

• Stability and Structure of Potentially Atmospherically Relevant Glycine Ammonium Bisulfate Clusters

  ChemRxiv · 2024-03-11

  preprintOpen accessSenior author

  New particle formation (NPF) is the process by which trace atmospheric acids and bases cluster and grow into particles that ultimately impact climate. Sulfuric acid concentration drives NPF, but nitrogen-containing bases promote the formation of more stable clusters via salt bridge formation. Recent computational efforts have suggested that amino acids can enhance NPF, predicting that they can stabilize new particles via multiple protonation sites, but there has yet to be experimental validation of these predictions. We used mass spectrometry and infrared spectroscopy to study the structure and stability of cationic clusters composed of glycine, sulfuric acid, and ammonia. When collisionally activated, clusters were significantly more likely to eliminate ammonia or sulfuric acid than glycine, while quantum chemical calculations predicted lower binding free energies for ammonia but similar binding free energies for glycine and sulfuric acid. These calculations predicted several low-energy structures, so we compared experimental and computed vibrational spectra to attempt to validate the computationally-predicted minimum energy structure. Unambiguous identification of the experimental structure by comparison to these calculations was made difficult by the complexity of the experimental spectra and the fact that the identity of the computed lowest-energy structure depended strongly on temperature. If their vapors are present, amino acids are likely to be enriched in new particles by displacing more weakly-bound ammonia, similar to the behavior of other atmospheric amines. The carboxylic acid groups were found to preferentially interact with other carboxylic acids, suggesting incipient organic/inorganic phase separation even at these small sizes.

  PublisherOA PDFDOI

• Photochemical Mechanisms in Atmospherically Relevant Iodine Oxide Clusters

  The Journal of Physical Chemistry Letters · 2024-06-10 · 2 citations

  articleSenior authorCorresponding

  Atmospheric new particle formation events can be driven by iodine oxides or oxoacids via both neutral and ionic mechanisms. Photolysis of new particles likely plays a significant role in their growth mechanisms, but their spectra and photolysis mechanisms remain difficult to characterize. We recorded ultraviolet (UV) photodissociation spectra of (I2O5)0–3(IO3–) clusters, observing loss of an O atom, I2O4, and (I2O5)1,2 in the atmospherically relevant range of 300–340 nm. With increasing cluster size, the intensity of absorption red shifts and generally increases, suggesting particles photolyze more frequently as they grow. Estimates of the rates indicate that even relatively small clusters are likely to undergo photolysis under high-UV conditions. Vibrational spectra identify the covalent moiety I3O8– as the likely chromophore, not IO3–. The I2O5 loss pathway competes with particle growth, while the slower O loss pathway likely produces 3O + 3(cluster) products that could drive subsequent intraparticle chemistry, particularly with co-adsorbed organic or amine species.

  PublisherDOI

• Resonance Effects from Substituents on L-Type Ligands Mediate Synthetic Control of Gold Nanocluster Frontier Orbital Energies

  The Journal of Physical Chemistry Letters · 2024-10-02 · 2 citations

  articleSenior authorCorresponding

  The ligands of metal nanoclusters can be used to control their properties and reactivity, but a framework guiding their use remains elusive. Hammett studies of Au8(PPh3)72+ and Au9(PPh3)83+ nanoclusters with para- and meta-methyl and -methoxy groups indicate that resonance effects, not inductive effects, yield quantitative shifts of the HOMO–LUMO transitions involving orbitals local to the cluster core. Individual ligand exchanges reveal that these shifts are caused by only four of seven ligands, inconsistent with inductive effects. Quantum chemical calculations predict no trend in Au atom charges with respect to Hammett parameter but do predict bond length trends expected for a resonance structure that includes the Au atoms. Computed orbitals show contributions from specific para-OMe oxygen lone pairs to the HOMO, indicating delocalization from the core to specific ligands. These results suggest that resonance structures could be drawn including Au and ligands, guiding efforts to modulate nanocluster electronic structure and energy transfer.

  PublisherDOI

• Stability and Structure of Potentially Atmospherically Relevant Glycine Ammonium Bisulfate Clusters

  ChemRxiv · 2024-03-12

  preprintOpen accessSenior author

  New particle formation (NPF) is the process by which trace atmospheric acids and bases cluster and grow into particles that ultimately impact climate. Sulfuric acid concentration drives NPF, but nitrogen-containing bases promote the formation of more stable clusters via salt bridge formation. Recent computational efforts have suggested that amino acids can enhance NPF, predicting that they can stabilize new particles via multiple protonation sites, but there has yet to be experimental validation of these predictions. We used mass spectrometry and infrared spectroscopy to study the structure and stability of cationic clusters composed of glycine, sulfuric acid, and ammonia. When collisionally activated, clusters were significantly more likely to eliminate ammonia or sulfuric acid than glycine, while quantum chemical calculations predicted lower binding free energies for ammonia but similar binding free energies for glycine and sulfuric acid. These calculations predicted several low-energy structures, so we compared experimental and computed vibrational spectra to attempt to validate the computationally-predicted minimum energy structure. Unambiguous identification of the experimental structure by comparison to these calculations was made difficult by the complexity of the experimental spectra and the fact that the identity of the computed lowest-energy structure depended strongly on temperature. If their vapors are present, amino acids are likely to be enriched in new particles by displacing more weakly-bound ammonia, similar to the behavior of other atmospheric amines. The carboxylic acid groups were found to preferentially interact with other carboxylic acids, suggesting incipient organic/inorganic phase separation even at these small sizes.

  PublisherOA PDFDOI

Recent grants

• Complex Acid-Base Chemistry in Minimal Solvation Environments - The Case of Atmospheric New Particle Formation

  NSF · $417k · 2016–2020

• MRI: Development of a Mass Spectrometer for Isomer-selective Thermochemical, Structural, and Spectroscopic Characterization of Bimolecular Interactions

  NSF · $1.1M · 2022–2027

• Laboratory Investigations of the Chemistry of Newly Formed Atmospheric Aerosols

  NSF · $200k · 2011–2013

• Establishing Water's Role in the Mechanism of Atmospheric New Particle Formation

  NSF · $445k · 2019–2023

Frequent coauthors

• Nicoline C. Frederiks

  Stony Brook University

  27 shared

• Mark A. Johnson

  26 shared

• Joseph A. Fournier

  Washington University in St. Louis

  21 shared

• Anthony E. G. Cass

  Imperial College London

  19 shared

• Robert E. Continetti

  University of California, San Diego

  17 shared

• John Kreinbihl

  Stony Brook University

  15 shared

• Conrad T. Wolke

  Carl Zeiss (Germany)

  14 shared

• Satavisha Sarkar

  State University of New York

  13 shared

Education

• Other

  CUNY Hunter College

• B.A.

  CUNY Hunter College

• M.A., Literature

  Columbia University

• B.S., Architecture

  MIT