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Pump and probe methods of laser spectroscopy, applied to monoisotopic mercury vapor contained in a quartz cell, were used to study the rotationally resolved G0+u ← A0+g system of excitation bands of the (202Hg)2 excimer. Sixty-nine rovibronic bands containing over 5700 rotational peaks were recorded and analyzed, yielding accurate values of spectroscopic constants that were employed in constructing RKR models of potential curves for the two states, permitting comparison with ab initio calculations.

Fluorescence and excitation spectra arising from transitions between excited states of the HgCd exciplex molecule were produced in a mixture of Hg and Cd vapors following pump-and-probe laser excitation. The vapor mixture, contained in a sealed quartz cell, was irradiated by pulsed pump (3261 \AA{}) and probe (4300\char21{}4750 \AA{}) laser beams, delayed by 450 ns relative to one another. The fluorescence bands were recorded with a monochromator, a photomultiplier, and a digitizing oscilloscope controlled by a microcomputer. In addition to the previously reported and analyzed ``blue-band'' fluorescence that can be excited with a single laser, we observed short-lived and structured fluorescence bands as well as the corresponding excitation bands in the blue spectral region, which we assigned to transitions between specific states of HgCd. An analysis of the bands yielded the vibrational constants for some of the states, as well as their relative internuclear equilibrium separations. These results provide an initial basis for the draft of a partial potential-energy diagram consisting of spin-orbit states correlated to the 5 $^{3}$P manifold in Cd.

The high-lying DO + , E1, and G1 spin—orbit states of the HgZn exciplex were excited by pump and probe laser irradiation of a HgZn vapor mixture in a quartz cell. The decays of these states gave rise to UV bound—free and visible bound—bound fluorescence spectra which were recorded with a monochromator, and scans of the probe dye laser produced excitation spectra in the region 4000–4600 A. Four new spectra were recorded and analyzed, yielding molecular constants for the various states. The new data also led to improved assignments of some previously reported HgZn spectra.

Isotopically pure 202Hg vapor, contained in a quartz cell, was irradiated with frequency-doubled 5140 A output from an Ar+ laser, which caused the formation of Hg2A0±g excimer molecules by photoassociation. Simultaneous probe radiation from a ring dye laser scanned over a range 5400–6000 A, produced the G0+u ← A0+g excitation spectrum which consists of several hundred well-resolved rotational components that have not been previously observed. Two vibronic bands were subjected to a rotational analysis which yielded spectroscopic constants that are compared with some previously reported values.

Pump and probe methods of laser spectroscopy were employed to excite several high-lying spin—orbit states of the HgZn exciplex. Their decays to lower bound vibronic states produced fluorescence spectra which were recorded with a monochromator in the region 4100–5200 A, and scans of the probe dye laser produced the corresponding excitation spectra. Six new spectra were recorded and analyzed, yielding molecular constants for the various states. The new data, together with a more recent version of the PE diagram, also led to improved assignments of some previously reported spectra.

5 3 P fine-structure mixing in Cd, induced in collisions in ground-state Hg atoms, was investigates by methods of LlF with time resolution. A quartz vapor-cell containing an HgCd mixture was irradiated with consecutive pump and probe laser pulses. The pump pulses (326.1 nm) produced a population of Cd 5 3 P 1 atoms whose collisions with Hg atoms caused the distribution of population among the 3 P fs states. These were probed with laser radiation exciting the 6 3 S 1 state which emitted fluorescence whose relative intensity was recorded in relation to the pum—probe delay, reflecting the time evolution of the respective 3 P J populations. The experiments which were carried out over a range of temperatures and CdHg densities, yielded the cross sections for the fs mixing collisions and the rate constant for the HgCd exciplex formation.

The 0 + u (4 1 P) state of Zn 2 was excited near the crossing of the 1 Σ + u (4 1 P) and 3 Π u (4 3 P) states, using pump and probe methods with time resolution. A structured excitation spectrum was observed in the 530–570 nm region and is ascribed to the 3 Π u (4 3 P)← 3 Π g (4 3 P) vibronic transitions. A fluorescence spectrum which was emitted in the 250–306 nm region is believed to arise from the 1 Σ + u →X 1 Σ + g bound—free decay. It consists of a “Condon internal diffraction pattern” whose profile suggests that it was emitted from a high vibrational level ( v ′ = 19) of the 1 Σ + u state.

The relative intensities of the vibrational components in the laser-induced fluorescence spectrum arising from a particular molecular vibronic state are usually independent of the exciting wave-length and thus do not depend on the lower vibronic state from which the excitation takes place. We have observed that although the intensity pattern in the fluorescence spectrum from the E0 − (ν'=0) level is independent of the excitation wavelength, the relative intensities of the bands in the fluorescence spectrum from the E0 − (ν'=1) level do depend on the wavelength of the exciting light. We have also observed that the vibrational intensity distribution in the excitation spectrum of the E0 − (ν'=1) level depends on the fluorescence wavelength at which it is monitored, whereas the intensity profile in the excitation spectrum of the E0 − (ν'=0) level is independent of the monitoring wavelength

Excitation and fluorescence spectra arising from bound-bound transitions between the E${0}^{\mathrm{\ensuremath{-}}}$ and the A1, A${0}^{\mathrm{\ensuremath{-}}}$, and B${0}^{\mathrm{\ensuremath{-}}}$ states of the HgZn excimer were investigated using pump-and-probe methods of laser spectroscopy. Several previously unknown bands were recorded, interpreted, and analyzed, yielding vibrational constants, relative energies, and relative internuclear separations for the various states.

Radiative transitions between the A2Π and X2Σ+ states of the ZnH molecule were induced using pump-and-probe methods of laser spectroscopy and resulted in the observation of several fluorescence and excitation bands with rotational structure. A time-evolution study of the fluorescence yielded the radiative lifetime τ0 = 47 ± 3 ns for the A2Π state; the cross section for quenching the A2Π, ν = 0 state by Zn collisions was estimated to be (2.4 ± 0.3) × 10−15 cm2. We also concluded that the ground-state ZnH molecule is a transient species that exists for approximately 10 μs.

A structured excitation spectrum of Zn2 in the 420–470 nm region was registered in zinc vapor subjected to pump-and-probe excitation as the emitted bound—free fluorescence was monitored at 274 nm. The excitation and fluorescence spectra were interpreted as due to transitions involving the 1Σ+u (5 1S), 3Πg (4 3P), and X1Σ+g (4 1S0) states. An analysis of the vibrational structure yielded vibrational constants and relative energies for the 1Σ+u and 3Πg states.

Fluorescence and excitation spectra of HgCd were studied using pump-and-probe methods of laser spectroscopy with time resolution. A Hg-Cd vapor mixture, contained in a sealed quartz cell at 700 K, was irradiated by consecutive pump and probe dye-laser pulses. The pump radiation produced a population of Cd 5 $^{3}$${\mathit{P}}_{1}$ atoms whose three-body collisions with Hg atoms resulted in the formation of HgCd excimers in the A${0}^{\mathrm{\ensuremath{-}}}$, A${0}^{+}$, and A1 states, correlated with the Cd 5 $^{3}$P+Hg 6 $^{1}$S manifold, which decayed, emitting a previously reported 4600-\AA{} fluorescence continuum. The probe pulses, delayed by 450 ns, excited the excimers to the higher-lying C${0}^{+}$ (Cd 5 $^{1}$${\mathit{P}}_{1}$+Hg 6 $^{1}$${\mathit{S}}_{0}$) state, which decayed to the repulsive X${0}^{+}$ ground state, emitting fluorescence in the 2400\char21{}2650-\AA{} region. We also observed a bound-bound excitation spectrum in the 5800\char21{}7100-\AA{} region. A study of the time evolution of the excimer fluorescence yielded an approximate value for the three-body rate coefficient for HgCd formation, and an analysis of the spectra produced spectroscopic constants for the states involved in the transitions.

Inelastic collisions of Cd 53P1 atoms with ground‐state Hg atoms were investigated by methods of LIF with time resolution. The experiments yielded the cross sections for mixing among the Cd 53P fs states and the rate constant for HgCd exciplex formation.

During a pump-and-probe spectroscopic study of the HgZn excimer, it was found that probing the Hg-Zn vapor cell with laser light in the 4200--4500-\AA{} range resulted in the intense emission of Hg 4916-\AA{} atomic fluorescence arising from the 8 $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6 $^{1}$${\mathit{P}}_{1}$ transition. This observation is ascribed to the predissociation of the HgZn F1 state through a curve crossing with the repulsive D${0}^{\mathrm{\ensuremath{-}}}$ state, followed by pooling collisions of the resulting Hg 6 $^{3}$P atoms, leading to the population of the 8 $^{1}$${\mathit{S}}_{0}$ state. This interpretation is corroborated by the results of spectroscopic and time-evolution experiments.

More extensive and much more precise spectroscopic data on the excitation of the G Ou+ state have led to an extended and improved analysis of the G Ou+ from A Og+ excitation band, yielding corrected assignments of vibrational components and revised values omega e=88 cm-1, omega ex epsilon =0.28 cm-1 for the G Ou+ state which supersede those published recently.

The G0u+ state in Hg2 'excimer' molecules (correlated with the 61P1 atomic state) was populated by stepwise excitation through the metastable A0g+ state, and the fluorescence emitted in the 0u+ to X0g+ decay was recorded with a spectrometer and a transient digitiser. The time evolution of the fluorescence indicated a very short ( approximately=1 ns) lifetime of the 0u+ excimer. The band corresponding to the v"=0(A0g+) to v'=0(G0u+) transition was identified in absorption and the energy separation of the two potential wells was determined as was the wavelength of the UV fluorescence emitted in the decay of the v'=0 level of the G0u+ state to the repulsive X0g+ ground state. A determination was made of the vibrational frequency omega 'e and the anharmonicity omega 'e chi 'e of the 0u+ state.

Cross sections for 7/sup 2/D/sub 3/2/bold-arrow-left-right7/sup 2/D/sub 5/2/ transfer in Rb, induced in collisions with He, Ne, Ar, and with ground-state Rb atoms, have been determined using methods of atomic fluorescence. Rb vapor, pure or mixed with a noble gas, was irradiated in a glass fluorescence cell with pulses of 660-nm radiation from a N/sub 2/-laser-pumped dye laser, populating one of the /sup 2/D states by two-photon absorption. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the collisionally populated state. Relative intensities of the components yielded the cross sections for 7/sup 2/D mixing: Q(/sup 2/D/sub 3/2/..-->../sup 2/D/sub 5/2/) = 8.8, 6.5, 10.4, and 30; Q(/sup 2/D/sub 3/2/reverse arrow/sup 2/D/sub 5/2/) = 5.8, 4.0, 6.9, and 18, in units of 10/sup -14/ cm/sup 2/ for He, Ne, Ar, and Rb, respectively. Cross sections for the effective quenching of the /sup 2/D states were also determined.

Cross sections for 7/sup 2/D and 8/sup 2/D fine-structure mixing in Rb, induced by collisions with various ground-state atoms and N/sub 2/ molecules, have been determined using methods of atomic fluorescence. Rb vapor, pure or mixed with a buffer gas, was irradiated in a glass fluorescence cell with pulses of radiation from a N/sub 2/ laser-pumped dye laser, populating a /sup 2/D fine-structure state by two-photon absorption. The resulting fluorescence included a direct component arising from the optically excited state and a sensitized component due to the collisionally populated fine-structure state. Measurements of relative intensities of the two components in relation to buffer-gas pressure yielded the following cross sections (in units of 10/sup -14/ cm/sup 2/): Q(7/sup 2/D/sub 3/2/..-->..7/sup 2/D/sub 5/2/) = 1 4.1, 15.5, and 10.0; Q(7/sup 2/D/sub 3/2/reverse arrow7/sup 2/D/sub 5/2/) = 9 .0, 10.5, and 6.9, for Kr, Xe, and N/sub 2/, respectively; Q(8/sup 2/D/sub 3/2/..-->..8/sup 2/D/sub 5/2/) = 8 .9, 4.9, 12.4, 24.9, 25.8, 12.1, and 43.1; Q(8/sup 2/D/sub 3/2/reverse arrow8/sup 2/D/sub 5/2/) = 5 .8, 3.2, 9.4, 15.1, 17.6, 8.3, and 28.5, for He, Ne, Ar, Kr, Xe, N/sub 2/, and Rb, respectively. Cross sections for the effective depopulation of the /sup 2/D states weremore » also determined.« less

Publisher Summary There has been a revival of interest in the spectroscopy of Group 2b excimers because of the possibility of laser action in the blue-green spectral region. In the past, various attempts to produce laser action in Hg2 have been unsuccessful because of excited-state absorption from either the upper laser-level or meta stable levels in equilibrium with it. The spectroscopy of the Hg2 excimer has been investigated systematically during recent years using pump method and probe method, and numerous bound excited states and transitions between pump method and probe method have been identified. Analysis of vibrational structures of the fluorescence and excitation bands yielded vibrational frequencies, anharmonicities, energy separations between the electronic states, and relative equilibrium inter nuclear separations. Recent high-resolution laser-spectroscopic studies of mono isotopic Hg 2 produced partial resolution of the rotational structure. Some non-linearity in the line-separations is due to the mode structure of the probe-laser output.

The 460 nm HgZn fluorescence band was excited by pumping a Hg‐Zn vapor mixture in a quartz cell with 307.59 nm laser pulses which populated the 43P1 Zn atomic state. The excited HgZn molecules were formed by collisions of the 43P1 Zn atoms with ground‐state Hg atoms. The resulting HgZn fluorescent band centered near 460 nm had a half‐width of about 80 nm and contained an additional component near 500 nm.

Pump-and-probe methods were used to excite high-lying I ( O u + ) and J(1 u ) states of Hg2, whose transitions to various lower states cause emission of fluorescence bands centered at 420 nm ( J 1 u → AO g ± ) , 513 nm (J1 u → E2 g ), 632.6 nm (J1 u → F1 g ), 451.4 nm ( I O u + → B 1 g ) , and 422.6 nm ( I O u + → A O g + ) . The transitions from I O u + and J(1 u ) to the repulsive X O g + ground state give rise to Condon internal diffraction patterns. A comprehensive investigation of the fluorescence bands and of the corresponding excitation spectra, some of which overlap, permitted unambiguous assignment of the bands to transitions between particular electronic states whose positions were located on the potential energy diagram. The experiment yielded vibrational constants for the molecular states as well as qualitative information about the relative internuclear separations for the various states.

Extensive and previously unknown fluorescence and excitation spectra of the HgZn excimer have been observed and correlated with a potential energy (PE) diagram. The spectra were excited in a HgZn mixture contained in a quartz vapor cell by successive pulses from two dye lasers using pump‐and‐probe methods. A vibrational analysis of the spectra yield the frequencies and anharmonicities for the states involved in the absorption and emission processes.

The continuum fluorescence bands of mercury at 335 and 485 nm have been known for over 50 years and it was recently shown that the 335 nm band is due to the D1u state of Hg2 [1] and the 485 nm band to the (math) state of Hg3 [2], There have also been several more recent reports of absorption and emission bands involving more highly excited states of Hg2 and Hg3 [2,3], which are now being extensively studied in this laboratory using LIF techniques combined with ‘pump and probe’ methods [4]. The fourth harmonic of a Q-switened Nd:YAG laser (266 nm) is focused into a quartz cell containing pure Hg vapor at densities 1017–1019 cm-3, to populate the metastable (math) Hg2 states. These were probed after a delay of 0.1 – 1 us with a second collinear pulse from a dye laser to produce more highly excited Hg2 states; a 5–10 us delay was required to produce similar Hg3 states. The fluorescence emitted in the decay of the various excited states was resolved with a monochromator and its time-evolution was registered with a transient digitizer. In this way we produced numerous fluorescence and excitation spectra whose analysis yielded accurate values of various molecular constants.

Several fluorescence and excitation bands, arising from transitions from and to the H, I, and J states of Hg/sub 2/, have been investigated using laser-induced fluorescence techniques. The upper and lower states have been assigned for each band and their analysis has yielded a number of vibrational constants. Measurements of relative intensities and studies of band shapes have made possible the accurate location of various electronic molecular states, relative to one another, on the potential energy diagram.