Andrew M. James

RESONANT TWO PHOTON IONIZATION SPECTROSCOPY OF THE MOLECULES V2, VNB AND NB2

Resonant two photon ionization (R2PI) spectroscopy was used to obtain detailed spectroscopic information on the neutral and cation ground states of the jet‐cooled molecules V2, VNb, and Nb2. By recording photoionization efficiency (PIE) spectra, their adiabatic ionization potentials were determined to be 51 269(5) cm−1 (V2), 51 554(10) cm−1 (VNb), and 51 359(10) cm−1 (Nb2). In VNb, we used different ionization routes to determine that the splitting between the Ω=0 and Ω=1 spin–orbit components of the X 3Σ− ground state was 230(3) cm−1. In the case of V2 and VNb, two thresholds were observed in the PIE spectra recorded via Ω=1 intermediate states. We were thus able to assign the ground states of V+2 and VNb+ as having 4Σ− symmetry, with second‐order spin–orbit splittings of 20(3) and 82(3) cm−1, respectively. A simple model was applied to calculate the locations of the 1Σ+ and 2Σ+ states which are responsible for the second‐order spin–orbit splitting of the neutral and cation ground states, respectively. O...

Electronic spectroscopy of the niobium dimer molecule: Experimental and theoretical results

Rotationally resolved electronic spectra of the niobium dimer molecule are reported for the first time. The molecules were produced by laser vaporization of a niobium target rod and cooled in a helium supersonic expansion. The molecular beam containing niobium dimer molecules was interrogated in the range 400–900 nm using a pulsed dye laser to excite fluorescence. Numerous Ω=0←Ω=0 and Ω=1←Ω=1 vibronic transitions were discovered in the region 630–720 nm and investigated at 200 MHz resolution using the cw output of a single mode ring dye laser. The principal features were classified into five Ω=0←Ω=0 systems originating from a common lower state of 0+g symmetry, and three Ω=1←Ω=1 systems originating from a common lower state of 1g symmetry. The two lower states were assigned as the Ω=0 and Ω=1 spin–orbit components of the X 3Σ−g ground state, which is derived from the electron configuration 1π4u1σ2g2σ2g1δ2g. The two spin–orbit components are split by several hundred cm−1 due to a strong, second‐order isoco...

PULSED FIELD IONIZATION ZERO KINETIC ENERGY PHOTOELECTRON SPECTROSCOPY OF THE VANADIUM DIMER MOLECULE

The technique of pulsed‐field‐ionization zero‐kinetic‐energy (PFI‐ZEKE), photoelectron spectroscopy was employed to probe the electronic structure of the V+2 cation. Rotationally resolved PFI‐ZEKE spectra of the V+2 ground state were obtained by two color excitation via the 700 nm A 3Πu←X 3Σ−g system. The observation of transitions from the A 3Π2u state to two spin–orbit components with Ω=1/2 and Ω=3/2, confirms that the cation ground state has 4Σg− symmetry, in accordance with previous experimental and theoretical work. Striking differences were observed in the rotational selection rules for the 4Σg−←A 3Π1u and the 4Σg−←A 3Π2u transitions. The adiabatic ionization potential of V2 was determined to be 51 271.14(50) cm−1. From an analysis of the rotational structure of the PFI‐ZEKE spectra, the following molecular constants were determined for the 4Σg− state: r0=1.7347(24) A, second order spin–orbit splitting, λ=5.248(17) cm−1, spin–rotation constant, γ=0.0097(87) cm−1, T0=51 282.20(50) cm−1 (1σ error bounds).

Pulsed field ionization zero kinetic energy photoelectron spectroscopy of small vanadium clusters. Using velocity slip as a mass selector

Abstract The pulsed field ionization zero kinetic energy photoelectron spectroscopy technique has been used to determine accurate ionization potentials for the small metal clusters V 3 and V 4 . Direct single-photon laser ionization was used. Assignment of the carrier of the photoionization spectra is aided by the velocity slip of the seeded cluster beam which provides a degree of mass separation in the neutral cluster molecules prior to ionization and, thereby, the ability to cross-correlate the PFI-ZEKE spectra with particular cluster species.

Spectroscopy of the indium argon van der Waals complex: A high resolution study of the B 2Σ1/2←X2 2Π3/2 system

The InAr van der Waals complex has been characterized by high resolution laser induced fluorescence excitation spectroscopy. Six vibronic bands of the B 2Σ1/2←X2 2Π3/2 transition have been observed and five of these (v’,0), where v’=1–5, have been rotationally analyzed. Rydberg–Klein–Rees potential curves were constructed for the B 2Σ1/2 state using the rotational and vibrational constants determined from these spectra. Equilibrium bond lengths were determined for the B and X2 states and a dissociation energy was determined for the B state. The stronger bonding present in the B state is rationalized in terms of penetration of the argon atom into the diffuse 6s orbital of indium. Evidence is presented that the B state potential energy curve has a barrier at long range, due to Pauli repulsion, of ∼60 cm−1. An analysis of the hyperfine structure involving the 115In nucleus was made. It is concluded that the X2 state conforms to Hund’s coupling case aβ, whereas the B state conforms to case bβs. The extent of ...

First observation of the VNb molecule

Abstract The electronic spectrum of VNb has been studied for the first time, using laser-induced fluorescence spectroscopy. Two band systems, with origins at 637.4 nm and 640.0 nm, were investigated at 200 MHz resolution, and involve Ω=0←Ω=0 and Ω=1←Ω=1 transitions respectively. We tentatively assign them as the case (a) allowed subbands of a 3Σ− ← X 3Σ− transition, where the lower state is the ground electronic state. The ground state bond length is determined to be re=1.93896(44) A.

Molecular beam Stark spectroscopy of the C 1Σ+–X 1Σ+ (0,0) band of yttrium monochloride

The yttrium monochloride molecule (YCl) has been produced in a free jet molecular beam apparatus by chemical reaction in a laser‐produced plasma. The origin band of the C 1Σ+–X 1Σ+ system of YCl was probed at the sub‐Doppler resolution of 120 MHz using a ring dye laser to excite fluorescence. Spectra due to the two isotopomers 89Y35Cl and 89Y37Cl were obtained, and molecular constants determined. The following bond lengths were derived (89Y35Cl):r0(X)=2.384 78(36) A, r0(C)=2.460 50(40) A (2σ error bounds). Results for the ground state are in good agreement with those recently reported by Xin et al. [J. Mol. Spectrosc. 148, 59 (1991)]. The permanent electric dipole moments for both the X and C states were determined by performing molecular beam Stark spectroscopy on the lines P(1) and R(0), respectively. Values of 2.587(29) D (X state) and 3.258(36) D (C state) were obtained. Results are compared with ab initio predictions of the molecular parameters, and a molecular orbital interpretation of the bonding i...

Molecular‐beam laser spectroscopy of lanthanum monofluoride: Magnetic hyperfine and dipole moment measurements

The lanthanum monofluoride molecule (LaF) was generated in a pulsed molecular beam by chemical reaction in a laser‐produced plasma. The (0,0) and (1,0) bands of the B 1Π–X 1Σ+ system of LaF (ν00=16 184.52 cm−1), and the 0+–X 1Σ+ band (ν00=16 637.95 cm−1), were investigated at sub‐Doppler resolution (120 MHz) using a ring dye laser to excite fluorescence. The electron orbital‐nuclear spin interaction parameter (magnetic hyperfine a parameter) was determined to be +138(5) MHz and +149(5) MHz for the v=0 and v=1 levels of the B 1Π state, respectively (2σ error bounds). The observed hyperfine structure is interpreted in terms of ligand field theory. Molecular rotational constants for all three bands were found to be in good agreement with previous work [Schall et al., J. Mol. Spectrosc. 100, 437 (1983)]. The permanent electric dipole moments of the X 1Σ+ and 0+ states of LaF were determined by molecular‐beam Stark spectroscopy to be 1.808(21) D and 3.43(10) D (2σ errors). Results are compared with recent expe...

Optical laser Stark spectroscopy of the yttrium monosulfide molecule

The yttrium monosulfide molecule was produced in a pulsed molecular beam apparatus by chemical reaction in a laser‐generated plasma. The permanent electric dipole moments of the X 2Σ+ and B 2Σ+ states were determined by molecular beam Stark spectroscopy to be 6.098(64) D and 4.572(92) D, respectively (2σ error bounds). Results are interpreted in terms of a molecular orbital description of the bonding. The experimental data are compared with dipole moment measurements for related molecules, and with the predictions of ab initio theory.

Stark effect measurement in samarium monoxide: Dipole moments of the (16.6)1 and X0− states

The permanent electric dipole moments of the [16.6]1 (the Ω=1 state lying near 16 600 cm−1) and X0− (ground) electronic states of 152SmO and 154SmO have been determined in a pulsed molecular beam by measuring the Stark shifts of the R(0) and R(1) lines of the (0,0) band in the [16.6]1–X0− transition. Electric fields up to 7.9 kV/cm were used. The Stark measurements also gave a precise determination of the Ω doubling of the J=1 level of the [16.6]1 state. The magnitudes of the dipole moments for the X0− and [16.6]1 states were determined to be 3.517(20) and 4.022(24) D for 152SmO, and 3.451(28) and 3.967(40) D for 154SmO (2σ error bounds). The splitting due to the Ω doubling of the J=1 level of the [16.6]1 state was determined to be 0.0433(24) cm−1 for 152SmO and 0.0380(50) cm−1 for 154SmO. A field dependent perturbation affecting the J=1, MJ=0 level of the [16.6]1 state of the 154SmO isotopomer was observed and analyzed.