pg 438, 450-453

Presence of absorption and emission spectra for various gaseous elements: Sodium, Nitrogen, Hydrogen, Oxygen.
Graphical representation: absorption and emission ranges from 450 nm to 700 nm.
- 450 nm: blue range
- 550 nm: green range
- 600 nm: orange range
- 650 nm: red range

Forensic scientists help solve analytical questions:
- Chemical composition of samples.
- Identifying mixtures vs. pure substances.
- Quantifying components in samples.
Spectroscopic methods provide rapid answers:
- Useful for determining elemental composition of substances.
- Understanding the elemental makeup aids in tracing origins and identities of forensic samples.

Qualitative Data: Indicates if a specific component exists in the sample.
- Example: Detection of arsenic in food, lead in paint, and iron in inks.
Quantitative Data: Measures the amount of a component present.
- Examples include:
- Analyzing alloy in crime scene bullets vs suspect's gun.
- Determining cocaine concentration in seized samples.
- Assessing beryllium levels in tissue samples for cause of death.
Atomic spectroscopy focuses on identifying and quantifying elements in samples through light interactions.

Ground State: Lowest energy state of an atom or molecule.
Excited State: Higher energy states of an atom or molecule than the ground state.
Emission: Transition where an electron falls from a higher energy state to a lower state, emitting light.
Absorption: Transition where an electron is promoted from a lower energy state to a higher state by absorbing energy.

Hydrogen Molecule (H₂): Contains two electrons in the lowest bonding molecular orbital.
Electrons must fill molecular orbitals based on quantum mechanics, with only two per orbital.

Encompasses the ultraviolet to visible spectrum (150 nm to 750 nm), sufficient for electron transitions within molecules (electronic spectroscopy).
Photon Absorption: Electrons transition from lower energy states (ground state) to higher states.
Emission: Similar to atomic spectra where electrons emit photons transitioning from high to low energy states.

Forensic analysis often employs UV-visible spectroscopy to identify organic compounds' functional groups.
- Certain groups absorb specific light wavelengths:
- For example: Aliphatic bromides absorb light around 205 nm; C=O units absorb around 290 nm.
Identifying functional groups aids in recognizing compound identity and concentration in forensic samples.
Color analysis in forensic investigations of paints, clothing, and other colored materials is facilitated by UV-visible spectroscopy.
- Rather than describing a color, forensic analysis can specify absorption peaks (e.g., absorption at 510 nm indicates a specific red from another red absorbing at 520 nm).

Deals not with electronic transitions, but with vibrational transitions due to infrared radiation, which has longer wavelengths than visible light.
Infrared energy excites quantized vibrations in chemical bonds, similar to compressing springs.
Vibrational Energy: Tied to the strength of the chemical bond and affected by factors like atomic identity and bonding types:
- Example of CO₂ regarding vibrational energy states.
To absorb infrared light, a change in the electronic center of charge must occur.

Vibrational States:
- Symmetric Stretch: O atoms move in/out simultaneously.
- Asymmetric Stretch: One O moves closer to C while the other moves away. This change allows absorption of IR light.
- Bending Modes: Similar to stretching, involve physical movement without bond breaking, also allow for IR absorption.
The IR spectrum shows only absorptions corresponding to allowed vibrations, showing that CO₂ is a simple molecule with specific vibrational characteristics.

Spectroscopy can enhance forensic methods, enabling identification of colors in various materials and detecting adjustments and restorations in fine artworks, establishing provenance and authenticity.
- Example: Analysis of works by Dirck Bouts reveals retouching through spectral techniques, allowing restorers insights into restoration needs.