Identification of hot band transitions of CH4 near 3000cm−1

Temperature dependence of rotational relaxation of methane in the 2ν3 vibrational state by self- and nitrogen-collisions and comparison with line broadening measurements

“…Owing to the results of hot band study [11], it was possible to probe also the other symmetry species of J = 1 as also the J = 0, F 2 , 18 state using lines of the 3m 3 (F 1 ) ‹ 2m 3 (F 2 ) band. The measurements for J = 1, E were performed by exciting methane into the 2m 3 (F 2 ) J = 1, E, 30 state and probing this level with the probe laser tuned to the R(1) line at 2959.61 cm À1 .…”

“…But the spectral width of the pumping laser does not allow us to select one line of the P(2) doublet that is used to excite into J = 1, E. However, as explained in Ref. [11], the symmetry of the rovibrational levels involved in the probed transition at 2959.61 cm À1 was determined by taking advantage of the fact that upon collision, state-to-state energy transfer can occur only between rotational levels of the same symmetry type, so that only levels of the same spin modification as the excited one may be filled through the energy redistribution over the tetradecad. By probing this transition, DR signals have been observed only after excitation of methane molecules via lines of 2m 3 (F 2 ) that have an E symmetry component.…”

“…For that, spectroscopic data on hot band transitions are needed. In our recent work [11] on methane, the DR technique appeared as a powerful tool to locate, in the spectral range near 3.4 lm, hot band vibration-rotation transitions involving a level of the 2m 3 (F 2 ) state of the tetradecad near 6000 cm À1 . Especially transitions between 2m 3 (F 2 ) and some vibrational sub-states of 3m 3 , whose energy is about 9000 cm À1 , have been observed and the quantum number J and the symmetry of the upper and lower rotational levels have been assigned without ambiguity for the first time.…”

First assignment of the 5ν4 and ν2+4ν4 band systems of 12CH4 in the 6287–6550cm−1 region

“…Despite many years of experimental and theoretical studies [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], the infrared methane spectrum is still insufficiently understood. In particular, the line-by-line analyses based on the expansion of an effective Hamiltonian and dipole moment, were able to provide precise data reductions only up to 4800 cm -1 [10,13,14].…”

Quantum state specific reactant preparation in a molecular beam by rapid adiabatic passage

“…For example, direct overtone pumping (i.e., a single photon transition) from the symmetric (A 1 ) ground state of CH 4 would only allow 2ν 3 to be prepared in the F 2 state. However, it is possible to prepare the A 1 , F 2 and E symmetry states by using double resonance excitation, [29][30][31] allowing a wider range of vibrational states to be studied. Using direct overtone pumping also results in a smaller fraction of the molecular beam being excited as the transition dipole moment is significantly smaller (μ = 1.0 × 10 −32 Cm 27 ).…”