Far infrared laser lines and assignments of CH3OH: a review

On the Assignment of Optically Pumped Far-Infrared Laser Emission from CH3OH

“…In the 9P(10) system, we still need to identify the source of the vibrational coupling leading to the hybridized (1,6) h E state (2), as well as the interaction partners for a number of localized level-crossing resonances in other systems. The mystery of a nearby hybrid partner has also surfaced for the (2,5) co A levels in the 9P(26) and 13-9R(26) systems. It seems fair to say that, while the methanol molecule may gradually be lifting the veils on its secrets, it continues to guard them well and to display remarkable resilience in posing challenging problems for spectroscopic study.…”

“…Our spectroscopic results, however, have revealed that the levels originally assigned as (2,5) co A have close hybridized companions lying just above, with subbands connecting to both partners from both (2,5) gr and (2,4) gr A lower states! The starting J values and relative intensities for the quartet of subbands suggest that at low J the lower partner actually has greater K ϭ 4 character, but we have not yet resolved this question and so will label the partner levels for the moment as the (2,5) hu A "up" and (2,5) hd A "down" members of hybridized doublets. The vibrational source for a K ϭ 4 state in this vicinity is by no means clear.…”

“…A pump assignment of P (1,Ϫ3,27) co E proposed earlier for this system (5,6,20), although plausible in several respects, has turned out to be wrong. The correct P(0, 9,27) co A pump assignment had escaped prior detection due to level-crossing resonances between the (0,9) and (1,5) A levels in both excited and ground vibrational states (11,49).…”

“…The correct P(0, 9,27) co A pump assignment had escaped prior detection due to level-crossing resonances between the (0,9) and (1,5) A levels in both excited and ground vibrational states (11,49). Perturbations occur first in the excited state as the interacting levels approach each other with increasing J; we have determined the [ (1,5) co -(0,9) co ] separations to be 0.133 and 0.184 cm Ϫ1 for JЈ ϭ 25 and 26, respectively. As the levels start to converge in the ground state at higher J, however, the shifts become quite erratic and we lose track of the subbands in the spectrum.…”

“…In the assignment put forward by Henningsen for this system (2), lasing was proposed from the (2,7,11) co E pumped level down to hybridized (1,6,11) h and (1,6,10) h E levels, with a further cascade from the latter down to the (1,5,9) co E level. We have identified both the (2,7) co and (1,6) h E subbands in the spectrum so we can confirm Henningsen's energy level and transition scheme.…”