An optical filter was situated between them to selectively monitor each mode. In the quadratic S2* sulfur mode, emission was routinely monitored using a 393 nm (12 nm bandpass) interference filter (Oriel Instruments,Stratford, USA). Conversely, the linear HSO* sulfur mode used 750 nm (40 nm bandpass) interference filter (Thorlabs, New-ton, USA), while the HPO* phosphorus mode employed a 527 nm(10 nm bandpass) interference filter (Melles Griot, Rochester,USA).