Collision induced deactivation of PH2(Ã 2A1;v2′=1,0) and PH2(X̃ 2B1;v2″=1) by diatomic molecules

Abstract

Deactivation of the bending mode v2′=1 and v2′=0 vibrational levels of PH2(Ã 2A1), and of the v2″=1 level of ground state PH2(X̃ 2B1) due to collisions with the diatomic molecules H2, N2, CO, and NO has been investigated. The Parmenter and co-worker’s, the Thayer and Yardley’s, and the collision complex theories have been used to rationalize the PH2(Ã 2A1) quenching data. Explanations for the deviations of the quenching data due to these molecular quenchers from the variation trend found, in a previous work, for the rare gas quenchers have been proposed. For the vibrational relaxation of PH2(X̃ 2B1;0,1,0), the data interpretation is based essentially on the theories by Schwartz, Slawsky, and Herzfeld–Tanczos, and Moore.

Collisional Deactivation of PH2(Ã2A1; v‘2 = 1,0) and PH2(X̃2B1; v‘ ‘2 = 1) by Some Triatomic Molecules

“…The deactivation constant of PH 2 ( v ‘ ‘ 2 = 1) by CO is factor 3.2 higher than that produced by N 2 of the same mass. As discussed in ref , this large difference cannot be explained neither by the dipole moment of CO which is rather weak, 0.1 D, nor by the difference in polarizability, 1.95 Å 3 for CO and 1.76 Å 3 for N 2 . Besides, CO and N 2 should deactivate v ‘ ‘ 2 = 1 through an intramolecular V−R,T mechanism, so the difference in energy mismatch between v ‘ ‘ 2 = 1 and CO (Δν = 1067 cm -1 ) on one hand, and between v ‘ ‘ 2 = 1 and N 2 (Δν = 1256 cm -1 ) on the other, which can be important in a V−V process, is of little help in this context.…”

“…Time-resolved fluorescence curves were collected, and their mathematical treatment to obtain the decay parameters have been extensively reported in previous papers …”

“…As there seems to be a correlation between the magnitude of the deviations and the vibrational frequencies of the diatomic quenchers, this additional channel has been assumed to be due to an intermolecular E−V process …”

“…The experimental setup has been described in detail in previous papers; 1,2 Fluorescence decay of PH 2 (A ˜2A 1 ; V′ 2 ) 0) and variation of (X ˜2B 1 ; V′′ 2 ) 0) concentrations were studied through excitation of the R Q 0 (7 17 -7 07 and 4 14 -4 04 ) rotational transitions of PH 2 (A ˜2A 1 ; V′ 2 ) 0-X ˜2B 1 ; V′′ 2 ) 0) system by 546.81 nm laser wavelength, whereas the (A ˜2A 1 ; V′ 2 ) 1) and (X ˜2B 1 ; V′′ 2 ) 1) species were monitored exciting the R Q 0 (6 16 -6 06 and 4 14 -4 04 ) transitions of PH 2 (A ˜2A 1 ; V′ 2 ) 1-X ˜2B 1 ; V′′ 2 ) 1) band with 551.33 nm radiation.…”

“…3 With the exception of the PH 3 molecule in self-quenching studies, 4 the molecular quenchers so far taken into consideration have been some diatomic molecules and in particular H 2 , N 2 , O 2 , CO, and NO. 1 The mechanism of interaction with the PH 2 species in both excited and ground electronic states has been seen to be different for each of them.…”