Nuclear quadrupole hyperfine quantum beats in HCl and pyrimidine measured by the pump-probe method using REMPI/LIF detection

Coherent time resolved IR-UV double resonance spectroscopy with REMPI and/o r LIF detection has been used to measure the nuclear hyperfine structure of a diatomic and a polyatomic molecule. The pump-probe technique was applied and the experimental set up was optimized to achieve highest spectral reso lution. Following excitation of the HCl fundamental vibrational transition by a nanosecond IR laser pulse, the nuclear quadrupole coupling constants w ere determined to be eQq = -69.51(22) MHz for H-35 Cl and cQq = -54.40(16) MHz for (HCl)-Cl-37 in the J = 1 and J = 2 states of the v = 1 level. Nucle ar (CI) spin-rotation interaction was shown to be active with the correspon ding coupling constant being CI = 0.068(10) MHz for (HCl)-Cl-35 and C-I = 0 .049(8) MHz for (HCl)-Cl-37. For pyrimidine a C-H stretch vibration vis was excited and the quadrupole tensor elements for the rovibronic states J(Ka, Kc) = 1(10) and 1(01) of the v(13) = 1 level were found to be X-aa = -3.095 (10) MHz, chi(bb) = 0.227(10) MHz and chi(cc) = 3.322(10) MHz. In this case the residual frequency error was reduced to 8 kHz. The results of these je t experiments independently confirm those from millimeter wave and microwav e measurements on static gas samples.