Shunji Kasahara

High resolution laser spectroscopy of the B 1Π–X 1Σ+ transition of 23Na85Rb

High resolution spectrum of the B 1Π–X 1Σ+ transition of the NaRb molecule was measured with the technique of the Doppler‐free laser polarization spectroscopy. Molecular constants of the B 1Π(v=0–12) and X 1Σ+(v=0–6) states of 23Na85Rb were determined. The energy levels of the B 1Π state were found to present many irregularities due to perturbations. The resonance fluorescence spectrum following an excitation to a strongly perturbed level was measured. The fluorescence to the (1)3Σ+ state, which consists of discrete lines followed by a continuum band, was observed in addition to the fluorescence lines to rovibrational levels of the X 1Σ+ state. The perturbing state to the B 1Π(v=8,J=15–21) levels is identified as the (1)3Π state by comparing the observed fluorescence spectra with the selection rules for perturbations and radiative transitions. The dissociation limit of the (1)3Σ+ state, which separates into the Na(3s2S1/2)+Rb(5s2S1/2) atoms, was deduced from the spectrum. The dissociation energies of the ...

Doppler-free optical–optical double resonance polarization spectroscopy of the 39K85Rb1 1Π and 2 1Π states

High resolution spectra of the 1  1 Π(v ′ =13–69,J ′ )←X  1 Σ + (v ″ ,J ″ ) and 2  1 Π(v ′ =0–13,J ′ )←X  1 Σ + (v ″ ,J ″ ) transitions of the 39 K 85 Rb molecule have been measured with the technique of Doppler-free optical–optical double resonance polarizationspectroscopy (OODRPS). Molecular constants of the 1  1 Π(v=13–69) and 2  1 Π(v=0–13) levels have been determined, and potential energy curves constructed by the RKR method. The RKR potential of the 1  1 Π state was found to have a distortion at outer wall, which originates from an avoided crossing of two 1 Π states. The perturbations between the 1  1 Π(v 1 ,J) and 2  1 Π(v 2 ,J) levels were found from the energy shifts of the rotational levels. The magnitude of the nonadiabaticinteraction between the 1  1 Π(v 1 =54) and 2  1 Π(v 2 =9) levels, 〈1  1 Π(v 1 =54)|T N |2  1 Π(v 2 =9)〉, was evaluated to be 2.2 cm−1 by a least squares fitting to the energy shifts of the 1  1 Π(v 1 =54,J=20–33) levels. The line intensities were observed to change dramatically around the maximum energy shift. These intensity anomalies are interpreted as an interference effect, which occurs when two interacting levels have comparable transition moments. A remarkable line broadening was observed for the transitions to the 1  1 Π(v⩾63) levels, and it was identified as originating from the predissociation to K (4s 2 S 1/2 )+ Rb (5p 2 P 1/2 ) atoms. The dissociation energies of the X  1 Σ + , 1  1 Π, and 2  1 Π states have been determined to be 4217.4±0.8, 2021.5±0.8, and 1050.0±0.8 cm−1, respectively.

Vibrational and rotational structure and excited-state dynamics of pyrene

Vibrational level structure in the S(0) (1)A(g) and S(1) (1)B(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S(1) (1)B(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0) (0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S(0) and S(1) states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M(J) levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S(0) state is also slow. We conclude that the similarity of pyrenes molecular structure and potential energy curve in its S(0) and S(1) states is the main cause of the slow radiationless transitions.

Doppler‐free high resolution laser spectroscopy of the Cs2 D 1Σ+u state and the predissociation

A Doppler‐free polarization spectrum of the D 1Σ+u(v’,J’)–X 1Σ+g(v‘,J‘) transition has been observed, and the molecular constants of the D 1Σ+u state were determined. A remarkable variation of the vibrational spacing ΔGv with v’, and large deviations of ΔGv from the fitted ΔGv curve for v’≳35 were analyzed. The potential curve of the perturbing state, which was identified as the bound (2)3Πu state, was estimated. By using an experimental setup where a collimated cesium beam is crossed at right angles by the laser beam, we measured the excitation spectra by monitoring separately the molecular fluorescence and the D2 or D1 atomic emission. We found that a predissociation of the D 1Σ+u state occurred for v’≳20, and the probability of predissociation increased with v’. The measured v’ and J’ dependence of the linewidth Γ showed a significant increase for v’≳25. The predissociation of the D 1Σ+u state is caused by a combination of spin–orbit interaction between the D 1Σ+u(v’J’) and (2)3Π0u(e vJ’) levels, and t...

Structure and excited-state dynamics of anthracene: Ultrahigh-resolution spectroscopy and theoretical calculation

Rotationally resolved ultrahigh-resolution spectra of the S(1) (1)B(2u)<--S(0) (1)A(g) transition of anthracene-h(10) and anthracene-d(10) have been observed using a single-mode UV laser and a collimated supersonic jet. We have determined rotational constants of the zero-vibrational levels of the S(0) and S(1) states by analyzing the precisely calibrated transition wavenumbers of rotational lines. We measured Zeeman splitting of each rotational line in the external magnetic field, of which the magnitude was small and strongly dependent on the rotational quantum numbers. We have shown that the magnetic moment in the S(1) (1)B(2u) state arises from J-L coupling with the S(2) (1)B(3u) state and that mixing with the triplet state is negligibly small. We concluded that the main radiationless transition in the S(1) state of anthracene is not intersystem crossing to the triplet state but internal conversion to the ground state. We also examined methods of ab initio theoretical calculation to determine which method most closely yielded the same values of rotational constants as the experimentally obtained ones. Moller-Plesset second-order perturbation method with a 6-31G(d,p) basis set yielded approximately the same values for the S(0) (1)A(g) state with an error of less than 0.04%. Geometrical structure in the S(0) (1)A(g) state of the isolated anthracene molecule has been accurately determined by this calculation. However, configurational-interaction with single excitations, time-dependent Hartree-Fock, and time-dependent density-function-theory methods did not yield satisfactory results for the excitation energy of the S(1) (1)B(2u) state. Symmetry-adapted-cluster configuration-interaction calculation was sufficiently good for the excitation energy and rotational constants.

High‐resolution laser spectroscopy of the X1Σ+ and (1)3Σ+ states of 23Na85Rb molecule

High‐resolution spectra of the B1Π→X1Σ+ transition of 23Na85Rb molecule are measured by the technique of the Doppler‐free optical–optical double resonance polarization spectroscopy (OODRPS). The molecular constants of the X1Σ+(v″=5−30) levels are determined, and the potential energy curve is constructed up to v″=30 by the RKR method. The time‐resolved fluorescence intensity following the excitation to the B1Π(v′=5,J′= around 20) level is measured, and the lifetime of the B1Π(v′=5) level in collisionless limit is determined to be 17.8 ns. The absolute value of the electric dipole moment of the B1Π−X1Σ+ transition is determined to be 7.0 D in the region of 3.73 A<R<4.98 A. Transition lines to the (1)3Σ+ state from the B1Π(v′=8,J′=15) level, which is perturbed by the (1)3Π1(v0,N=J=15) level, are measured by the Doppler‐free OODRPS. The energy spacing between the F1 and F3 components of the (1)3Σ+(v=4,N=15) level is observed to be smaller than 0.001 cm−1. The hyperfine splittings, which are described by Hund’...

Optical–optical double resonance polarization spectroscopy of the B 1Π state of 39K85Rb

High resolution spectra of the B 1Π←X 1Σ+ transition of the 39K85Rb molecule have been measured with the technique of Doppler‐free optical–optical double resonance polarization spectroscopy. Molecular constants of the B 1Π(v′=0−12) levels are determined, and the RKR potential is calculated. A number of irregularities in the energies of B 1Π state levels and intensity anomalies are observed. The energy shifts of the e and f levels of the B 1Π state are studied, and the perturbations between the B 1Π and 3Σ+ states and between the B 1Π and 3Π1 states are identified. Several transitions to the 3Π1 and 3Σ+ states are also observed, and the molecular constants of the 3Π1 and 3Σ+ states are evaluated. The single rovibrational level B 1Π(v′=2, J′=41) is selectively excited by a single frequency laser chopped by an electro‐optical modulator, and the decay time of the resulting fluorescence is measured at various pressures. From the Stern–Volmer plot, the radiative lifetime and the collisional cross section of the...

Doppler-free two-photon absorption spectroscopy of the A1Au←X1Ag transition of trans-glyoxal

Doppler-free two-photon absorption spectra of the A1Au←X1Ag(π*−n) transition of trans-glyoxal have been measured by means of two-photon absorption spectroscopy with counter-propagating light beams of identical photons within an external cavity. The relative energies of transition lines are measured with accuracy better than 0.0001 cm−1. Rotational lines are fully resolved, and 1809 lines of the A1Au(v7=1)←X1Ag(v=0) transition are assigned for J=0−75,K=0−17. Rotational constants of the A1Au(v7=1) and X1Ag(v=0) states are determined by a least-squares fitting of eigenvalues of the A-reduced rotational Hamiltonian to energies of the assigned lines. Energy shifts, intensity anomalies, and line splittings are observed for several lines. When an external magnetic field is applied, remarkable changes are observed for these lines. They are identified as originating from perturbations between the A1Au and a3Au states, which become appreciable when perturbing levels are close in energy. Splittings into three lines ...

High resolution laser spectroscopy up to the dissociation limit of the NaK B 1Π state, and predissociation near the dissociation limit

Doppler‐free high resolution spectrum of the B 1Π(v’,J’)–X 1Σ+(v‘,J‘) transitions of 23Na39K was measured by the optical–optical double resonance (OODR) polarization spectroscopy. The transition lines up to the v’=43 level, which was estimated to be 1.8 cm−1 below the dissociation limit, were observed. The potential energy curve for internuclear distance from 3.25 to 15.6 A was calculated by the RKR method, and the inverse‐power coefficient was determined by analyzing the long‐range RKR turning points. The B 1Π state dissociates to Na(3s2S1/2)+K(4p2P3/2) atoms without a potential hill near the dissociation limit. The dissociation energy was determined to be 1324.3±0.3 cm−1 from the LeRoy–Bernstein plots. Remarkable line broadenings were observed for transitions higher than the dissociation energy to Na(3s2S1/2)+K(4p2P1/2) atoms. This is identified as originating from the predissociation to Na(3s2S1/2)+K(4p2P1/2) atoms. The predissociation is shown to be caused by a spin–orbit interaction between the B 1Π ...

High-resolution spectroscopy of weak and short-lived bands of the S1 B13u←S0 A1g transition of naphthalene

Rotationally resolved high-resolution spectra and fluorescence decay curves have been observed for weak and short-lived vibronic bands of the S(1) (1)B(3u) <-- S(0) (1)A(g) transition of naphthalene. Fluorescence lifetime of the vibronic band with an excess energy of 1390 cm(-1) (0(0)(0) + 1390 cm(-1) band) is remarkably shorter than that of other bands. Zeeman splitting of rotational lines is very small, so that the main radiationless process is not intersystem crossing to the triplet state but internal conversion to the ground state. The lifetime is thought to be governed by the strength of vibronic coupling between vibrational levels of the S(0) and S(1) states. As for the 0(0)(0) + 2570 cm(-1) band, energy shifts were found in only a few rotational levels although the excess energy was higher than the threshold of intramolecular vibrational redistribution. We conclude that all of the rotational levels are mixed with other vibrational levels. The 0(0)(0) + 3068 cm(-1) band spectrum is fairly complicated with numerous rotational lines, which is attributed to strong vibronic coupling with the S(2) (1)B(2u) state.