Cavity Ringdown Spectroscopy (CRDS)

CRDS measures the loss of light travelling between two highly reflective parallel (super)mirrors. In a properly aligned cavity light can be reflected thousands of times, greatly increasing the traveled path-length and thus making even the weakest absorptions observable. Radicals and ions are generated using an electrical discharge of a precursor gas in the throat of a slit nozzle. Typically a mixture of low concentration acetylene in helium is used. By skimming part of the plasma downstream and extracting the ions into a mass spectrometer the chemical composition of the beam is determined.

The group's CRD setup utilizes a pulsed dye laser with a minimal linewidth of 0.05 cm^–1. With this resolution the rotational structure of molecules as large as HC₈H⁺ can be resolved. The pulsed dye laser, pumped by an excimer or Nd:YAG laser, can cover the whole visible range, from 280–850 nm. With this apparatus a variety of carbon chains terminated with hydrogen, nitrogen and sulfur have been observed, with sizes ranging from 4 to 12 atoms. Cyclic B₃, C₃H₅ (allyl) and other radicals and various positive ions have also been studied.

Selected publications:

• Ranjini Raghunandan, Fabio J.Mazzotti, and John P. Maier
  J. Am. Soc. Mass Spectrom., 21(5), 694–697, 2010.
  Electronic Spectra of C₆H⁺ and C₆H₃⁺ in the Gas Phase
  
• Fabio J. Mazzotti, Richa Chauhan, Zahra Jamshidi, Marek Tulej, Peter P. Radi, and John P. Maier
  Mol. Phys., 106(24), 2709–2715, 2008.
  The òΠ_3/2 – X²Π_3/2 electronic transition of HC₄S isotopologues
  
• Elena Achkasova, Mitsunori Araki, Alexey Denisov, and John P. Maier
  J. Mol. Spectrosc., 237(1), 70–75, 2006.
  Gas phase electronic spectrum of propadienylidene C₃H₂
  
• Tomasz Motylewski and Harold Linnartz
  Rev. Sci. Instrum., 70(2), 1305–1312, 1999.
  Cavity ring down spectroscopy on radicals in a supersonic slit nozzle discharge
  
• Harold Linnartz, Tomasz Motylewski, and John P. Maier
  J. Chem. Phys., 109(10), 3819–3823, 1998.
  The ²Π←X ²Π electronic spectra of C₈H and C₁₀H in the gas phase