Supersonically expanded sodium metal-dilute halogen gas interactions. The importance of reaction populated and energy storing reservoir states and population inversion created amplification in Na2.

The reactions of Cl, Br, and I with Nan=2,3 produced in a supersonic expansion form Na2* and Na* excited states extending across the visible and ultraviolet regions. Emission in the region extending from 410 to 600 nm indicates selectively formed excited state Na2 emission features. Experimental evidence suggests that this emission is associated with Na3 + X reactions. Broadband (0.5 cm-1) laser measurements demonstrate gain (population inversion) for select features at∼524-528(1%), ∼492(0.3%), and ∼458.7-461(0.8%) nm. Single mode (0.007 cm-1) measurements extending from 528.03 to 527.63 nm demonstrate amplification involving five to six individual rovibronic levels with a maximum gain close to 3% recorded at 527.9 nm. The observed gain is associated with select transitions from levels of the Na2 11Πu state populated, via identified curve crossings, through collision induced transfer from long-lived Na2 21Σg+ and 11Πg reservoir states. Collision induced population buildup in the lowest vibrational levels of these reservoir states and collision induced transfer to the Na2 11Πu state create a population inversion in transitions to the X 1Σg+ state of Na2. The observed amplification is aided by rapid vibrational and rotational relaxation in both the Na2 ground and excited reservoir states producing amplifiers in the visible region like the HF amplifier in the infrared. This study suggests the importance of reaction populated and energy storing long-lived reservoir states in small sodium molecule combustion processes and indicates the potential for providing new short wavelength visible and ultraviolet amplifiers for future laser-based chemical propulsion concepts.