Direct observation of coherent rotational excitation, dephasing and depopulation of methanol and its isotopes using THz pulse radiation

Abstract

Coherent transients are directly observed in the time-domain as a sequence of decreasing commensurate pulses in methanol (CH3OH) and its isotopes (CH3OD and CD3OD) gases to yield fundamental information on its dephasing and depopulation. The delay times between coherent pulses of ∼21, 22, and 26ps are measured for the CH3OH, CH3OD, and CD3OD corresponding to the inverse of rotational energy spacing for ΔJ=±1 transitions, respectively. The dephasing time T2=23±0.5ps and depopulation time T1=48±0.5ps were measured for CH3OH at room temperature.