Pressure broadening and collisional narrowing in OH(v=1←0) rovibrational transitions with Ar, He, O2, and N2

Abstract

Line shapes are measured for OH(v=1←0) transitions in the presence of Ar, He, O2, and N2 as a function of N rotational, spin–orbit, and λ doublet states. Pressure broadening coefficients for all transitions and buffer gases are determined from fits of the observed line shapes to the Voigt profile. The dependencies of the observed broadening coefficients on the OH quantum levels are discussed and compared with previous pressure broadening studies in HF and NO. The observed OH line shapes are interpreted in terms of their impact on the determination of mesospheric and stratospheric OH populations, temperatures, and quantum state distributions from OH nightglow and dayglow emission. In the case of OH+Ar, evidence for Dicke narrowing is presented and narrowing coefficients are reported from fits to a ‘‘hard collision’’ model.

Pressure broadening and shifting of vibrotational lines of atmospheric gases

“…On the mesosphere level, OH is formed in excited vibrational states (v ≤ 9) by the reaction Н+О 3 and relaxes to the ground state during the night. Emission spectra of OH were recorded in the mesosphere for the rotational numbers N ≈ 33 [230] (the total angular momentum of the molecule…”

“…Experimental determination of OH absorption line profiles was realised for broadening by N 2 , O 2 , NO 2 , He, Ar and Kr in the near IR region, by Н 2 О and NО 2 in the microwave region and by N 2 and rare gases in the UV region [230][231][232][233][234][235][236]. In Ref.…”

“…In Ref. [230], the broadening coefficients of OH lines by N 2 , O 2 , He and Ar pressure were extracted for the P-branch of the fundamental (1-0) band using the Voigt profile model (Table 4.55). For Ar-broadening the profile of Rautian and Sobel'man was equally tested, yielding γ and β 0 coefficients (Table 4.56).…”

“…Ar-broadening and narrowing coefficients (in MHz Torr -1 ) obtained with the Rautian-Sobel'man profile for the P-branch of the ОН band v = 1 ← 0[230]. Reproduced with permission.…”

Pressure broadening calculations for OH in collisions with argon: Rotational, vibrational, and electronic transitions

“…To our knowledge, there has been only one experimental investigation of collisional effects in the infrared spectrum of OH. Schiffman and Nesbitt [9] determined room-temperature pressure broadening coefficients for lines in the P branches of the v=1 ← v=0 vibrational transition in collisions with He, O 2 , and N 2 . In the case of Ar as a collision partner, evidence for Dicke narrowing was found, and the line shapes were analyzed in terms of a "hard collision" model to extract pressure broadening coefficients and Dicke narrowing parameters.…”