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Proceedings Paper

New ways to optically detect CH2 and HCF radicals using resonance-enhanced multiphoton ionization spectroscopy
Author(s): Jeffrey W. Hudgens; Russell D. Johnson; Karl K. Irikura
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Paper Abstract

We report two new optical detection methods for the CH2 (X 3B1) radical and one new detection method for the HCF (X 1A') radical. These detection methods are based upon resonance enhanced multiphoton ionization (REMPI) spectroscopy and require only commonly available lasers. Single laser pulse sensitivity for CH2 and HCF is better than 108 radicals(DOT)cm-3. REMPI spectra of CH2 between 380 and 440 nm arose from three-photon resonances with the B 3A2 (3d), C (3d), D (3d), and 4d 3A2 Rydberg states between 78,950 and 68,200 cm-1 above the ground state. A fourth laser photon ionized the radicals and the signal was carried by CH2+ (m/z 14) ions, i.e., CH2 signal arises through a 3 + 1 REMPI mechanism. We have also discovered two new states, H(3p) and I(4p), that enable extremely sensitive detection of CH2 through a 2 + 1 REMPI scheme. In two photons, the H(3p) state produces a strong band at 311.80 nm (64,126 cm-1). The much weaker I(4p) state appears at 269.27 nm (74,254 cm-1). Between 305 and 325 nm HCF and DCF radicals produce 2 + 1 REMPI spectra by excitation to 3p Rydberg states. The band origins for HCF and DCF are at 321.6 nm (62,180 cm-1) and 321.7 nm, respectively.

Paper Details

Date Published: 22 April 1993
PDF: 7 pages
Proc. SPIE 1858, Laser Techniques for State-Selected and State-to-State Chemistry, (22 April 1993); doi: 10.1117/12.143083
Show Author Affiliations
Jeffrey W. Hudgens, National Institute of Standards and Technology (United States)
Russell D. Johnson, National Institute of Standards and Technology (United States)
Karl K. Irikura, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 1858:
Laser Techniques for State-Selected and State-to-State Chemistry
Cheuk Yiu Ng, Editor(s)

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