Abstract

Frequency-modulation spectroscopy (FMS)^1-3 is a sensitive form of derivative absorption spectroscopy. The technique was used with two diode-laser systems to study the fundamental and second-overtone transitions of hydrogen iodide. A lead-salt diode laser operating at 4.7μm was used to measure the line strengths and nitrogen-collisional-broadening coefficients of the P-branch of the fundamental transition. For the second overtone, a near-IR system using a single-mode InGaAs laser was used, and several transitions of the R-branch were measured. The high sensitivity of our system (1 × 10^-6) facilitated the measurement of high covibrational (J = 18) transitions. The dipole-moment function and Herman-Wallis coefficients of HI were calculated, on the basis of the line strength measurements.

© 1990 Optical Society of America