Code shared from the Rust Playground

playground.rs

// Cargo.toml dependencies:
// serde = { version = "1.0", features = ["derive"] }
// chrono = "0.4"
// rand_0_8_5 = { package = "rand", version = "0.8.5" }

use serde::Serialize;
use std::collections::HashMap;

/// Speed of light (c) in m/s
const C: f64 = 299_792_458.0;

#[derive(Debug, Serialize)]
struct SpectralLine {
    wavelength_nm: f64,
    frequency_thz: f64,
}

impl SpectralLine {
    fn new(nm: f64) -> Self {
        // f = c / lambda
        let freq_hz = C / (nm * 1e-9);
        Self {
            wavelength_nm: nm,
            frequency_thz: freq_hz / 1e12,
        }
    }
}

fn main() {
    let mut periodic_table_lines: HashMap<&str, Vec<f64>> = HashMap::new();

    // Mapping prominent persistent lines (nm) for various elements from the image
    periodic_table_lines.insert("Hydrogen", vec![656.3, 486.1, 434.1, 410.2]); // Balmer Series
    periodic_table_lines.insert("Helium", vec![587.6, 667.8, 501.6, 447.1]);
    periodic_table_lines.insert("Lithium", vec![670.8, 610.4, 460.3]);
    periodic_table_lines.insert("Mercury", vec![546.1, 435.8, 404.7, 579.1]);
    periodic_table_lines.insert("Neon", vec![585.2, 640.2, 614.3, 540.1, 703.2]);
    periodic_table_lines.insert("Sodium", vec![589.0, 589.6]); // The famous D-lines
    periodic_table_lines.insert("Titanium", vec![498.1, 499.1, 500.7, 365.3]);
    periodic_table_lines.insert("Gold", vec![479.2, 583.7, 627.8]);

    println!("{:<10} | {:<20} | {:<20}", "Element", "Wavelength (nm)", "Frequency (THz)");
    println!("{:-<55}", "");

    // Iterate through all stored elements
    for (element, lines) in &periodic_table_lines {
        for nm in lines {
            let line = SpectralLine::new(*nm);
            println!(
                "{:<10} | {:<20.2} | {:<20.2}",
                element, line.wavelength_nm, line.frequency_thz
            );
        }
        println!("{:-<55}", "");
    }

    // Logic Note:
    // To print ALL ~100,000 lines from the NIST database, you would typically 
    // parse a CSV/JSON export from NIST ASD (Atomic Spectra Database).
}