Density measurements in air by optically exciting the Cordes bands of I₂

Abstract

We describe an optical method based on laser-induced fluorescence for obtaining instantaneous measurements of density along a line in low-density air seeded with I2 . The Cordes bands of I2 (D 1 u + X 1 g + ) are excited with a tunable ArF excimer laser. Air densities in the range (0.1 - 6.5) × 1017 cm-3 are measured over 295 - 583 K using the density-dependent emission ratio of two emission bands of I2 ; the 340 nm bands and the diffuse-structured McLennan bands near 320 nm.

Thermometry in air by optically exciting the I2Cordes bands

“…The experiment was described previously [16]; it is summarized here. A schematic diagram of the experiment is shown in figure 1.…”

“…D to D transfer in air is temperature independent with an estimated rate constant of ∼10 −10 cm 3 s −1 [16]. Hence it occurs with nearly unit collision efficiency.…”

“…There is 1 I 2 -I 2 collision with 1 × 10 15 cm −3 I 2 during the D-state lifetime of 15.5 ns. Previous studies [16,28] have shown that D-state removal requires only a single buffer-gas collision. This indicates negligible collisional redistribution.…”

“…This method detected 3 × 10 12 cm −3 I 2 in 1.8 × 10 17 cm −3 air. Balla and Exton [16] measured air densities from 0.1 to 6.5 × 10 17 cm −3 over 295-583 K instantaneously along a line. This method used density-dependent emission from two I 2 electronic states.…”

Fluorescence imaging and streakline visualization of hypersonic flow over rapid prototype wind-tunnel models

“…PLIF has already been used for visualization and quantitative measurement in wake flows in hypersonic facilities using excitation of NO [4][5][6], as well as I 2 [7]. NO PLIF is complementary to I 2 PLIF -the two methods having different seeding requirements and offering different measurement capabilities [8][9][10][11]. NO PLIF is the approach used in the current work.…”