Dynamical symmetry breaking in the 4νCH rovibrational manifold of acetylene

Rovibrational Energy Transfer in the 4νCHManifold of Acetylene Viewed by IR−UV Double Resonance Spectroscopy. 2. Perturbed States withJ= 17 and 18

“…71 (A very weak feature at ∼323.1 nm, in the bottom trace of Figure 4, is apparently associated with J ) 0, but this cannot be confirmed by combination differences since (1 0 3 0 0) 0 J ) 0 can only be prepared by P(1) IR pump excitation in the (ν 1 + 3ν 3 ) band; moreover, J ) 0 reduced term values generated for this feature do not match any predicted subbands for ν′ 2 , ν′ 3 , or ν′ 4 /ν′ 6 , so that the feature is possibly due to an accidental overlap of the IR pump with another intermediate level (V, J, K), as has been found in other instances.) 28,29,32 Reduced term value plots 32 have been used to tentatively assign the rovibronic features for J ) 12 and 14-24 in Figure 4 as P, Q, or R. However, assignment of K′ is omitted, since that quantum number is not a well-defined label for the Α -state rovibronic levels accessed in these IR-UV DR spectra (owing primarily to b-axis Coriolis coupling). 32,81 The righthand Q-branch feature at 323.791 nm in the J ) 12 trace of Figure 4 was used for UV probe excitation in the IR-scanned IR-UV DR spectra presented in Figure 1.…”

“…These include J ) 17 (see section IV below), J ) 19 (see Figure 8 of ref 76, where use of narrowband IR pump and UV probe sources yield no fresh insight into odd-∆J RET), and J ) 23 and 24. 32,33 As in previous experiments, [28][29][30][34][35][36][37] it is always important to ensure that a given IR-UV DR rovibronic feature is uniquely characteristic of its designated rovibrational J-state, avoiding accidental coincidences that might lead to spectroscopic ambiguities and thereby hinder reliable interpretation.…”

“…Apart from these IR-UV DR investigations of the 12 700 cm -1 4ν CH manifold of C 2 H 2 , [28][29][30]32,33 we have also studied IR-UV DR spectroscopy and collision-induced energy-transfer dynamics in its 11 600 cm -1 (ν CC + 3ν CH ) manifold. [34][35][36][37] This complements other LIF-detected IR-UV DR studies of C 2 H 2 and its isotopomers in overtone/combination levels with high vibrational energy (G v > 6500 cm -1 ) [38][39][40][41][42][43] and fundamental and lower-energy overtone or combination levels (G v e 6500 cm -1 ).…”

“…Such odd-∆J energy transfer is understood to be possible in the presence of some forms of intramolecular and/or collision-induced rovibrational perturbations that are prevalent in the high-energy vibrational manifold of C 2 H 2 . [28][29][30][32][33][34][35][36][37] The IR-UV DR spectrum in trace a is recorded under effectively collision-free conditions with a very small collision number z. (As before, [28][29][30][34][35][36][37]47 values of z are referred arbitrarily to Lennard-Jones collisional rate constants k LJ that are consistent with those adopted by Crim and co-workers; 38,39 for C 2 H 2 /C 2 H 2 self-collisions at 300 K, k LJ ) 16.4 µs -1 Torr -1 ) 5.10 × 10 -10 cm 3 molecule -1 s -1 .)…”

“…[28][29][30][32][33][34][35][36][37] The IR-UV DR spectrum in trace a is recorded under effectively collision-free conditions with a very small collision number z. (As before, [28][29][30][34][35][36][37]47 values of z are referred arbitrarily to Lennard-Jones collisional rate constants k LJ that are consistent with those adopted by Crim and co-workers; 38,39 for C 2 H 2 /C 2 H 2 self-collisions at 300 K, k LJ ) 16.4 µs -1 Torr -1 ) 5.10 × 10 -10 cm 3 molecule -1 s -1 .) The simple spectrum in trace a comprises the (ν 1 + 3ν 3 )-band R(11) peak; it is accompanied by a single P(13) peak beyond the low-frequency limit of Figure 1, thereby confirming that the UV probe pulse is indeed monitoring the (1 0 3 0 0) 0 J ) 12 rovibrational level.…”