Data and Technical Details

Data Description

When a molecule is excited (e.g., by electron collision in a plasma), it will decay from a higher energy level (upper level) to a lower energy level (lower level) undergoing a downward transition and release a photon with a precise wavelength which depends on the energy difference between the two levels, E = E_upper - E_lower = hν = hc/λ. It is the spectral fingerprint of a molecule, since each molecular species (and its specific excited state) possesses a distinct pattern of emission lines. Owing to the coupling of electronic, vibrational, and rotational degrees of freedom, molecular transitions typically give rise not to isolated lines, but to band spectra—clusters of closely spaced lines resulting from simultaneous changes in vibrational and rotational quantum numbers during an electronic transition.

Each emission line includes:

  • Molecule - Chemical formula (e.g., CO, H2, OH)

  • System - Spectroscopic transition notation

  • Wavelength - In nm and Ångström

  • Upper/Lower Level - Energy state notation

  • Intensity - Relative intensity (when available)

  • Source - Literature reference and page number

Technical Implementation

Architecture

  • Frontend: HTML/CSS/JavaScript

  • Visualization: Chart.js library

  • Data: Static JSON files

  • Hosting: GitHub Pages (Jekyll)

MELT is entirely client-side - all data processing happens in your browser. No server required.

Spectrum Generation

Emission lines are modeled as Gaussian peaks:

\[I(\lambda) = I_0 \cdot \exp\left(-\frac{(\lambda - \lambda_0)^2}{2\sigma^2}\right)\]

Where:

  • λ₀ = line center wavelength

  • I₀ = peak intensity

  • σ = standard deviation (related to FWHM by: FWHM = 2.355σ)

File Structure

MELT/
├── index.html              # Main application
├── assets/
│   ├── js/
│   │   └── molecular-lines.js   # Core logic
│   └── data/
│       ├── data-manifest.json   # List of all data files
│       ├── Pearse&Gaydon/       # Pearse & Gaydon (1976) data
│       ├── 1985_Borucki.json    # Borucki et al. (1985)
│       ├── 1996_Clay.json       # Clay et al. (1996)
│       ├── 2008_Camacho.json    # Camacho et al. (2008)
│       ├── 2008_Reyes.json      # Reyes et al. (2008)
│       ├── 2014_Rezaei.json     # Rezaei et al. (2014)
│       ├── 2015_Kiristi.json    # Kiristi et al. (2015)
│       └── 2022_Zhang.json      # Zhang et al. (2022)
└── docs/                   # This documentation

Data Files

JSON format, one file per molecule:

[
  {
    "molecule": "CO",
    "system": "d³Δ–a³Π",
    "wavelength_nm": 646.46,
    "wavelength_angstrom": 6464.6,
    "upper_level": "d³Δ",
    "lower_level": "a³Π",
    "intensity": null,
    "source": "Pearse & Gaydon (1976) p.111",
    "page": 111
  }
]

Adding New Databases

To contribute additional spectroscopic data:

  1. Format data as JSON following the schema above

  2. Validate JSON syntax

  3. Test in local copy of MELT

  4. Submit via GitHub pull request

See Development for detailed instructions.

Limitations

  • Intensity data not always available (shown as null)

  • Wavelength precision varies by source (typically 0.01-0.1 nm)

  • Temperature dependence not specified

  • Line shapes modeled as Gaussian (real shapes may differ)

For absolute intensity measurements or high-precision work, consult original sources.

References

Data sources:

  • Pearse, R. W. B., & Gaydon, A. G. (1976). The identification of molecular spectra (4th ed.). Chapman & Hall.

  • Borucki, W. J., McKenzie, R. L., McKay, C. P., Duong, N. D., & Boac, D. S. (1985). Spectra of simulated lightning on Venus, Jupiter, and Titan. Icarus, 64(2), 221-232. https://doi.org/10.1016/0019-1035(85)90087-9

  • Clay, K. J., Speakman, S. P., Amaratunga, G. A. J., & Silva, S. R. P. (1996). Characterization of a-C:H:N deposition from CH4/N2 rf plasmas using optical emission spectroscopy. Journal of Applied Physics, 79(9), 7227-7233. https://doi.org/10.1063/1.361439

  • Camacho, J. J., Díaz, L., Santos, M., Reyman, D., & Poyato, J. M. L. (2008). Optical emission spectroscopic study of plasma plumes generated by IR CO2 pulsed laser on carbon targets. Journal of Physics D: Applied Physics, 41(10), 105201. https://doi.org/10.1088/0022-3727/41/10/105201

  • Reyes, P. G., Mendez, E. F., Osorio-Gonzalez, D., Castillo, F., & Martínez, H. (2008). Optical emission spectroscopy of CO2 glow discharge at low pressure. physica status solidi c, 5(4), 907-910. https://doi.org/10.1002/pssc.200778306

  • Rezaei, F., Abbasi-Firouzjah, M., & Shokri, B. (2014). Investigation of antibacterial and wettability behaviours of plasma-modified PMMA films for application in ophthalmology. Journal of Physics D: Applied Physics, 47(8), 085401. https://doi.org/10.1088/0022-3727/47/8/085401

  • Kiristi, M., Bozduman, F., Oksuz, A. U., Hala, A., & Oksuz, L. (2015). A Comparison Study of Microwave and Radio Frequency Plasma Polymerized PEDOT Thin Films. Journal of Macromolecular Science, Part A, 52(2), 124-129. https://doi.org/10.1080/10601325.2015.980762

  • Zhang, S., Zeng, X., Bai, H., Zhang, C., & Shao, T. (2022). Optical emission spectroscopy measurement of plasma parameters in a nanosecond pulsed spark discharge for CO2/CH4 dry reforming. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 267, 120590. https://doi.org/10.1016/j.saa.2021.120590

Additional resources: