title: Torsionally mediated spin-rotation hyperfine splittings at moderate to high J values in methanol.
abstract: This paper presents an explanation based on torsionally mediated proton-spin-overall-rotation interaction for the observation of doublet hyperfine splittings in some Lamb-dip sub-millimeter-wave transitions between ground-state torsion-rotation states of E symmetry in methanol. These unexpected doublet splittings, some as large as 70 kHz, were observed for rotational quantum numbers in the range of J = 13 to 34, and K = - 2 to +3. Because they increase nearly linearly with J for a given branch, we confined our search for an explanation to hyperfine operators containing one nuclear-spin angular momentum factor I and one overall-rotation angular momentum factor J (i.e., to spin-rotation operators) and ignored both spin-spin and spin-torsion operators, since they contain no rotational angular momentum operator. Furthermore, since traditional spin-rotation operators did not seem capable of explaining the observed splittings, we constructed totally symmetric "torsionally mediated spin-rotation operators" by multiplying the E-species spin-rotation operator by an E-species torsional-coordinate factor of the form e(±niα). The resulting operator is capable of connecting the two components of a degenerate torsion-rotation E state. This has the effect of turning the hyperfine splitting pattern upside down for some nuclear-spin states, which leads to bottom-to-top and top-to-bottom hyperfine selection rules for some transitions, and thus to an explanation for the unexpectedly large observed hyperfine splittings. The constructed operator cannot contribute to hyperfine splittings in the A-species manifold because its matrix elements within the set of torsion-rotation A1 and A2 states are all zero. The theory developed here fits the observed large doublet splittings to a root-mean-square residual of less than 1 kHz and predicts unresolvable splittings for a number of transitions in which no doublet splitting was detected.
authors.affiliation: Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov Street, 603950 Nizhny Novgorod, Russia.
authors.forename: S P
authors.initials: SP
authors.lastname: Belov
authors.affiliation: Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov Street, 603950 Nizhny Novgorod, Russia.
authors.forename: G Yu
authors.initials: GY
authors.lastname: Golubiatnikov
authors.affiliation: Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov Street, 603950 Nizhny Novgorod, Russia.
authors.forename: A V
authors.initials: AV
authors.lastname: Lapinov
authors.affiliation: Institute of Radio Astronomy of National Academy of Sciences of Ukraine, Chervonopraporna 4, 61002 Kharkov, Ukraine.
authors.forename: V V
authors.initials: VV
authors.lastname: Ilyushin
authors.affiliation: Institute of Radio Astronomy of National Academy of Sciences of Ukraine, Chervonopraporna 4, 61002 Kharkov, Ukraine.
authors.forename: E A
authors.initials: EA
authors.lastname: Alekseev
authors.affiliation: Institute of Radio Astronomy of National Academy of Sciences of Ukraine, Chervonopraporna 4, 61002 Kharkov, Ukraine.
authors.forename: A A
authors.initials: AA
authors.lastname: Mescheryakov
authors.affiliation: Sensor Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8441, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Hougen
authors.affiliation: Department of Physics and Centre for Laser, Atomic, and Molecular Sciences, University of New Brunswick, Saint John, New Brunswick E2L 4L5, Canada.
authors.forename: Li-Hong
authors.initials: LH
authors.lastname: Xu