Richard A. Gottscho

Deperturbation of the N2+ first negative group B2Σu+-X2Σg+

Abstract Twelve bands of the N 2 + B 2 Σ u + - X 2 Σ g + system, including v B = 0–6 and v X = 0–8, are reanalyzed. All effects of B 2 Σ u + ∼ A 2 Π u perturbations are explicitly considered. Despite the use of high precision (0.01 cm −1 ) line measurements, no evidence for a perturber other than A 2 Π u is obtained. Deperturbed constants for the B 2 Σ u + and X 2 Σ g + states are derived. The deperturbation is shown to be self-consistent and complete (excluding effects of the C 2 Σ u + state) by examining semiempirical relationships of the perturbation matrix elements with the spin-rotation constants of the B and X states and atomic spin-orbit parameters. A number of previous analyses of transitions involving the v B = 3 and 5 levels are found to be incorrect.

Global analysis of the NaNe excimer band systems: A molecule between Hund’s cases

We have least‐squares fit 244 transitions in the mutually perturbing NaNe A 2Π–X 2Σ+ and B 2Σ+–X 2Σ+ excimer band systems using a Hund’s case ’’c’’ basis. Interatomic potentials were determined by matching computed spectroscopic parameters to 43 fitted parameters. This deperturbation analysis implies that the Na atomic angular momentum qunatum numbers—L and S—are also good molecular quantum numbers. NaNe exhibits an intramolecular transition from Hund’s case c to Hund’s case ’’a’’ angular momentum coupling as the internuclear distance is decreased. The nature of this transition is mediated by the shapes, depths, and positions of both the A 2Π and B 2Σ+ van der Waals potentials.

OODR spectroscopy of BaO. II. New observations of a 3Π and A′ 1Π and re‐examination of the Parkinson band system

One and two dye lasers have been used in an optical–optical double resonance (OODR) study of the excited B 1Π and C 1Σ+ states as well as the low‐lying, long‐lived A′ 1Π and a 3Π1 electronic states of BaO. C 1Σ+ (v=0) is shown to be the upper level in the v′=0 progression of the Parkinson band system. Intensity anomalies in C 1Σ+–X 1Σ+ emission, due to an interference effect between parallel and perpendicular transition amplitudes, have proved to be a sensitive indication of ΔΩ=±1 perturbations. Emission from C 1Σ+, which is populated by absorption of two photons via a real intermediate A 1Σ+ vibronic level, into A′ 1Π (v=0,1, and 2) and a 3Π1 (v=0,1, and 2) has been observed. A scheme is presented by which the relative populations of the A′ 1Π and a 3Π ’’reservoir states’’ could be monitored.

Collisional depolarization of state selected (J,MJ) BaO A 1Σ+ measured by optical–optical double resonance

The optical–optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares A 1Σ+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the C 1Σ+ state. Elastic collisions (ΔJ = 0) between BaO (A 1Σ+) and CO2 are observed to change M from 0 to ±1 leaving J unchanged. The total elastic M‐changing cross section is σΔMCO2 = 8.4±2.4 A2. Inelastic collisions (ΔJ = +1’ which transfer molecules to j = 2 also cause M changes. with both Ar and CO2 as collision partners. M, the space‐fixed projection of J, is found to be neither conserved nor randomized. Quantum atom–diatom collision models with quantization axis along the relative velocity vector are considered. Transition amplitudes in this system are evaluated us...

Laser spectroscopy of the diatomic van der Waals molecule NaNe

We present a thorough spectroscopic study of the van der Waals molecule NaNe. Our molecular beam apparatus, laser scanning system, and frequency reference technique are described in detail. Methods of rotational analysis are discussed. Descriptions of the observed vibration–rotation bands in the A 2Πr–X 2Σ+ and B 2Σ+–X 2Σ+ manifolds are presented. Perturbations in the observed spectra are discussed. Long range analysis techniques are used to determine the vibrational quantum numbering from observed isotopic shifts and to determine excited and ground state potential parameters. We find DeA=145±05 cm−1 at ReA=5.1(1)a0, DeX=8.1(9) cm−1 at ReX=10.0(1)a0, and DeB?3.0(5) cm−1 at ReB?14.4(3)a0.

High resolution spectra of bands of the first negative group of ionized molecular nitrogen (N2+ 1NG: B2Σu+ → X2Σg+)

Abstract The emission spectrum of the First Negative Group of ionized molecular nitrogen ( N 2 + 1 NG : B 2 Σ u + → X 2 Σ g + ) has been photographed at high resolution in the spectral region from 3800 to 4750 A. Lines have been identified as arising from the following bands: (0,0), (1,1); (0,1), (1,2), (2,3); (0,2), (1,3), (2,4), (3,5), (4,6), (5,7), and (6,8). The absolute accuracy of the measurements is approximately 0.01 cm−1, with relative rrecision between close lines in a given band of 0.005 cm−1. A complete line list is presented. Preliminary results of a spectral analysis are given, and the accuracy of final molecular constants is estimated. A complete analysis will be contained in a subsequent paper.

Observed and calculated interactions between valence states of the NO molecule

Abstract No perturbation between two valence states of NO has ever been identified, although many valence-Rydberg and several Rydberg-Rydberg perturbations have been extensively studied. The first valence-valence crossing to be experimentally documented for NO is reported here and occurs between the 15 N 18 O B 2 Π ( v = 18) and B ′ 2 Δ ( v = 1) levels. No level shifts larger than the detection limit of 0.1 cm −1 are observed at the crossings near J = 6.5 [B 2 Π (F 1 ) ∼ B′ 2 Δ (F 2 )] and J = 12.5 [B 2 Π (F 1 ) ∼ B′ 2 Δ (F 1 )] ; two crossings involving higher rotational levels could not be examined. Semi-empirical calculations of spin-orbit and Coriolis perturbation matrix elements indicate that although the electronic part of the B 2 Π ∼ B′ 2 Δ interaction is large, a small vibrational factor renders the 15 N 18 O B ( v = 18) − B ′ ( v = 1) perturbation unobservable. Semi-empirical estimates are given for all perturbation matrix elements of the operators Σ i a i l i ·s i and B(L ± S ⊣ − J ± L ⊣ ) which connect states belonging to the configurations (σ2p) 2 (π2p) 4 (π ∗ 2p) , (σ2p)(π2p) 4 (π ∗ 2p) 2 , and (σ2p) 2 (π2p) 3 (π ∗ 2p) 2 .

Optical-Optical Double-Resonance Spectroscopy of CaF

Abstract Optical-optical double-resonance (OODR) induced photoluminescence into the lowest excited electronic states of BaO— a 3 Σ + , A 1 Σ + , b 3 Π, and A′ 1 Π —from C 1 Σ + is described. These low-lying states are deperturbed to obtain spectroscopic constants and potential energy curves: a 3 Σ + A 1 Σ + b 3 Π A′ 1 Π T e ( cm −1 ) 16 596(3) 16 807.345(10) 17 502.6(10) 17 619.7(2) ω e ( cm −1 ) 469.0(7) 499.620(19) 447.62(8) 447.95(22) ω e x e ( cm −1 ) 1.48(4) 1.716(8) 2.287(12) 2.139(8) ω e y e × 10 2 ( cm −1 ) 2.14(9) 1.02(3) B e ( cm −1 ) 0.2594(5) 0.2583908(26) 0.22426(16) 0.22385(16) α e × 10 3 ( cm −1 ) 1.44(5) 1.111(3) 1.18(4) 1.15(4) γ e × 10 6 ( cm −1 ) 7.0(7) −4.0(21) R e ( A ) 2.1294(20) 2.133512(11) 2.2901(8) 2.2922(8) where uncertainties of 1σ are given in parentheses. The results of this deperturbation suggest the presence of additional low-lying, Δ states which perturb b 3 Π and A′ 1 Π .

Simultaneous measurement of rotational and translational relaxation by sub‐Doppler optical–optical double resonance spectroscopy: BaO(A 1Σ+)–Ar and BaO(A1Σ+)–CO2

Sub‐Doppler optical–optical double resonance (OODR) spectroscopy is used to correlate BaO(A1Σ+) rotational and translational relaxation induced by collisions with Ar or CO2 in a 0.3–2 Torr Ba+CO2+Ar flame. A selected rovibronic BaO A 1Σ+←X 1Σ+ transition is pumped by the first of two frequency stabilized, 1 MHz bandwidth, cw dye lasers. Collision‐induced level‐to‐level processes in the A 1Σ+ state are monitored with the second laser by excitation of C 1Σ+←A1Σ+ probe transitions and detection of C 1Σ+→X 1Σ+ ultraviolet fluorescence. The dependence of J‐changing collision rates on the initial A 1Σ+ (v=1) rotational level, Jo, is monitored by independent preparation of Jo=0 and Jo=15. For Ar, ‖ΔJ‖=1–20 collision rates are found to be independent of Jo and well represented by the power law, where ΔEr is the change in BaO (A 1Σ+) rotational energy in cm−1; e=ΔEr for Jo<J and e=0 for Jo≳J. For BaO∼CO2 collisions a single power law is inadequate to represent Jo=0 and Jo=15 data: Total BaO–Ar J‐changing collision...

Valence states of the SiS molecule: Analysis of perturbations in the A1Π-X1Σ+ system

Abstract The results of a detailed rotational analysis of bands of the A 1 Π- X 1 Σ + systems both of 28 SiS and of 30 SiS are given. Perturbations caused by interactions with two singlet states, D 1 Δ and C 1 Σ − , and with two triplet states, e 3 Σ − and d 3 Δ, are analyzed. The use of three different methods, based (i) on Franck-Condon factors, (ii) on isotope shifts, and (iii) on the identification of perturbing levels which cross more than one vibrational level of A 1 Π, to determine the vibrational numbering in the perturbing states is examined and for three of the above electronic states an unambiguous numbering is derived. Two alternative consecutive vibrational numberings for D 1 Δ are suggested. Method (i) is unreliable here, because of the very high vibrational quantum numbers of the levels that perturb A 1 Π. RKR potentials are constructed and thence, with calculated Franck-Condon factors, values of the electronic interaction constants are derived for the interactions between the perturbing states and A 1 Π. The values so obtained are compared with those for CO, CS, and SiO, and with estimates from ab initio calculations.