Fluorescence excitation spectra of the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u), and c(n) (') (1)Sigma(u) (+) states of N(2) in the 80-100 nm region

Fluorescence excitation spectra produced through photoexcitation of N(2) using synchrotron radiation in the spectral region between 80 and 100 nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115-320 nm and 300-700 nm regions, respectively. The peaks in the vacuum ultraviolet fluorescence excitation spectra are found to correspond to excitation of absorption transitions from the ground electronic state to the b (1)Pi(u), b(') (1)Sigma(u) (+), c(n) (1)Pi(u) (with n=4-8), c(n) (') (1)Sigma(u) (+) (with n=5-9), and c(4) (')(v('))(1)Sigma(u) (+) (with v(')=0-8) states of N(2). The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. Fluorescence peaks, which correlate with the long vibrational progressions of the c(4) (') (1)Sigma(u) (+) (with v(')=0-8) and the b(') (1)Sigma(u) (+) (with v(') up to 19), have been observed. The present results provide important information for further unraveling of complicated and intriguing interactions among the excited electronic states of N(2). Furthermore, solar photon excitation of N(2) leading to the production of c(4) (')(0) may provide useful data required for evaluating and analyzing dayglow models relevant to the interpretation of c(4) (')(0) in the atmospheres of Earth, Jupiter, Saturn, Titan, and Triton.     

Predissociation mechanism for the lowest 1 Pi u states of N2

Separate coupled-channel Schr?dinger-equation (CSE) models of the interacting (1)Pi(u) (b,c,o) and (3)Pi(u) (C,C(')) states of N(2) are combined, through the inclusion of spin-orbit interactions, to produce a five-channel CSE model of the N(2) predissociation. Comparison of the model calculations with an experimental database, consisting principally of detailed new measurements of the vibrational and isotopic dependence of the (1)Pi(u) linewidths and lifetimes, provides convincing evidence that the predissociation of the lowest (1)Pi(u) levels in N(2) is primarily an indirect process, involving spin-orbit coupling between the b (1)Pi(u)- and C (3)Pi(u)-state levels, the latter levels themselves heavily predissociated electrostatically by the C(') (3)Pi(u) continuum. The well-known large width of the b(v=3) level in (14)N(2) is caused by an accidental degeneracy with C(v=9). This CSE model provides the first quantitative explanation of the predissociation mechanism for the dipole-accessible (1)Pi(u) states of N(2), and is thus likely to prove useful in the construction of realistic radiative-transfer and photochemical models for nitrogen-rich planetary atmospheres.     

Interactions of the 3ppi u c1Pi u(v=2) Rydberg-complex member in isotopic N2

The 3ppi u c1Pi u-X 1Sigmag+(2,0) Rydberg and b' 1Sigmau+-X 1Sigmag+(7,0) valence transitions of 14N2, 14N15N, and 15N2 are studied using laser-based 1 extreme ultraviolet (XUV)+1' UV two-photon-ionization spectroscopy, supplemented by synchrotron-based hotoabsorption measurements in the case of 14N2. For each isotopomer, effective rotational interactions between the c(v=2) and b'(v=7) levels are found to cause strong Lambda-doubling in c(v=2) and dramatic P/R-branch intensity anomalies in the b'-X(7,0) band due to the effects of quantum interference. Local perturbations in energy and predissociation line width for the c(v=2) Rydberg level are observed and attributed to a spin-orbit interaction with the crossing, short-lived C 3Pi u(v=17) valence level.     

The spin-orbit and rotational constants for the N2 C" 5Pi(ui) (v = 3) state

The spin-orbit (A = -16.4 cm(-1)) and rotational (B = 1.017 cm(-1)) constants for the N2 C" 5Pi(ui)(v = 3) level are determined by a fit to rotational lines in the C" 5Pi(u)-A' 5Sigma(g)+(3-1) band that terminate in J'Omega' = 3(3), 4(3), 3(2), and 4(2) levels of the C" state. The C"-state spin-orbit constant is consistent with semi-empirical estimates, based on spin-orbit constants observed in several other electronic states of N2 and the atomic spin-orbit coupling constant, zeta(N 2p). The C"-A' bands exhibit the unusual feature of oppositely degraded sub-band heads, Omega' = 3 (red) and Omega' = 1, 0, and -1 (blue). The unusually wide range of B(Omega)eff values, from 0.85 cm(-1) (Omega = 3) to 1.28 cm(-1) (Omega = -1) for C" 5Pi(v = 3) should be diagnostically useful for Omega'-assignments. The C" 5Pi(v = 3) level lies 14257.17 and 90599 cm(-1) above A' 5Sigma(g)+(v = 1) and X 1Sigma(g)+(v = 0), respectively, and Re(C" 5Pi) = 1.50 A.     

Rotational effects in the band oscillator strengths and predissociation linewidths for the lowest 1Pi u-X 1Sigmag+ transitions of N2

A coupled-channel Schrodinger equation (CSE) model of N2 photodissociation, which includes the effects of all interactions between the b, c, and o 1Pi u and the C and C' 3Pi u states, is employed to study the effects of rotation on the lowest-upsilon 1Pi u-X 1Sigmag+(upsilon,0) band oscillator strengths and 1Pi u predissociation linewidths. Significant rotational dependences are found which are in excellent agreement with recent experimental results, where comparisons are possible. New extreme-ultraviolet (EUV) photoabsorption spectra of the key b 1Pi u<--X 1Sigmag +(3,0) transition of N2 are also presented and analyzed, revealing a b(upsilon=3) predissociation linewidth peaking near J=11. This behavior can be reproduced only if the triplet structure of the C state is included explicitly in the CSE-model calculations, with a spin-orbit constant A approximately 15 cm(-1) for the diffuse C(upsilon=9) level which accidentally predissociates b(upsilon=3). The complex rotational behavior of the b-X(3,0) and other bands may be an important component in the modeling of EUV transmission through nitrogen-rich planetary atmospheres.     

Observation and calculation of the Cs2 2 3Delta(1g) and b 3Pi(0u) states

The Cs(2) 2 (3)Delta(1g) and b (3)Pi(0u) states have been observed by infrared-infrared double resonance spectroscopy for the first time. 221 2 (3)Delta(1g)<--A (1)Sigma(u) (+)<--X (1)Sigma(g) (+) double resonance lines have been assigned to transitions into the 2 (3)Delta(1g) v=6-13 vibrational levels. Resolved fluorescence into the b (3)Pi(0u) v(')=0-48 levels has been recorded. Molecular constants and potential energy curves are determined by the global fit of the entire set of the experimental data. Theoretical potential energy curves of the 2 (3)Delta(g) and b (3)Pi(u) states have been determined in the framework of the pseudopotential method and are compared with the experimental results.     

The d (3)Pi(g)-c (3)Sigma(u) (+) band system of C2

A two-dimensional fluorescence (excitation/emission) spectrum of C2 produced in an acetylene discharge was used to identify and separate emission bands from the d (3)Pi(g)<--c (3)Sigma(u) (+) and d (3)Pi(g)<--a (3)Pi(u) excitations. Rotationally resolved excitation spectra of the (4<--1), (5<--1), (5<--2), and (7<--3) bands in the d (3)Pi(g)<--c (3)Sigma(u) (+) system of C2 were observed by laser-induced fluorescence spectroscopy. The molecular constants of each vibrational level, determined from rotational analysis, were used to calculate the spectroscopic constants of the c (3)Sigma(u) (+) state. The principal molecular constants for the c (3)Sigma(u) (+) state are B(e)=1.9319(19) cm(-1), alpha(e)=0.018 55(69) cm(-1), omega(e)=2061.9 cm(-1), omega(e)x(e)=14.84 cm(-1), and T(0)(c-a)=8662.925(3) cm(-1). We report also the first experimental observations of dispersed fluorescence from the d (3)Pi(g) state to the c (3)Sigma(u) (+) state, namely, d (3)Pi(g)(v=3)-->c (3)Sigma(u) (+)(v=0,1).     

Oscillator strengths and line widths of dipole-allowed transitions in (14)N(2) between 89.7 and 93.5 nm

Line oscillator strengths in the 20 electric dipole-allowed bands of (14)N(2) in the 89.7-93.5 nm (111480-106950 cm(-1)) region are reported from photoabsorption measurements at an instrumental resolution of approximately 6 mA (0.7 cm(-1)) full width at half maximum. The absorption spectrum comprises transitions to vibrational levels of the 3p sigma(u) c(4)' (1)Sigma(u)(+), 3p pi(u) c(3) (1)Pi(u), and 3s sigma(g) o(3) (1)Pi(u) Rydberg states and of the b' (1)Sigma(u)(+) and b (1)Pi(u) valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled Schrodinger-equation calculations. Most bands in this study are characterized by a strong J dependence of the band f values and display anomalous P-, Q-, and R-branch intensity patterns. Predissociation line widths, which are reported for 11 bands, also exhibit strong J dependences. The f value and line width patterns can inform current efforts to develop comprehensive spectroscopic models that incorporate rotational effects and predissociation mechanisms, and they are critical for the construction of realistic atmospheric radiative-transfer models.     

Observation of the d3Pi(g)<--c3Sigma(u)+ band system of C2

A new band system of C(2), d (3)Pi(g)<--c (3)Sigma(u) (+) is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the c (3)Sigma(u) (+) state of C(2). Observations were made by laser excitation of c (3)Sigma(u) (+)(v(")=0) C(2), produced in an acetylene discharge, to the d (3)Pi(g)(v(')=3) level, followed by detection of Swan band fluorescence. Rotational analysis of this band yielded rotational constants for the c (3)Sigma(u) (+)(v(")=0) state: B(0)=1.9218(2) cm(-1), lambda(0)=-0.335(4) cm(-1) and gamma(0)=0.011(2) cm(-1). The vibrational band origin was determined to be nu(3-0)=15861.28 cm(-1).     

Optical observation of the 3s sigma gF3Pi u Rydberg state of N2

Using ultrahigh-resolution 1 XUV+1 UV two-photon ionization laser spectroscopy, the F (3)Pi(u)<--X (1)Sigma(g) (+)(0,0) transition of N(2) has been optically observed for the first time, and the 3s sigma(g)F (3)Pi(u)(upsilon=0) Rydberg level fully characterized with rotational resolution. The experimental spectroscopic parameters and predissociation level widths suggest strong interactions between the F state and the 3p pi(u)G (3)Pi(u) Rydberg and C(') (3)Pi(u) valence states, analogous to those well known in the case of the isoconfigurational (1)Pi(u) states.     

Oscillator strength and linewidth measurements of dipole-allowed transitions in 14N2 between 93.5 and 99.5 nm

Line oscillator strengths in 16 electric dipole-allowed bands of 14N2 in the 93.5-99.5 nm (106,950-100,500 cm(-1)) region have been measured at an instrumental resolution of 6.5 x 10(-4) nm (0.7 cm(-1)). The transitions terminate on vibrational levels of the 3psigma 1Sigma u (+), 3ppi 1Pi u, and 3ssigma 1Pi u Rydberg states and of the b' 1Sigma u (+) and b 1Pi u valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled-Schrodinger-equation calculations that do not take into account rotational interactions. Most bands in this study reveal a marked J dependence of the f values and/or display anomalous P-, Q- and R-branch intensity patterns. These patterns should help inform future spectroscopic models that incorporate rotational effects, and these are critical for the construction of realistic atmospheric radiative transfer models. Linewidth measurements are reported for four bands. Information provided by the J dependences of the experimental linewidths should be of use in the development of a more complete understanding of the predissociation mechanisms in N2.     

Experimental study of the NaK 3 3Pi double minimum state

We have used the Doppler-free, perturbation-facilitated optical-optical double-resonance technique to investigate the vibrational, rotational, and hyperfine structure of the 3 (3)Pi double minimum state of NaK. Since this electronic state arises from an avoided crossing with the nearby 4 (3)Pi state, we observe striking patterns in the data that provide a sensitive probe of the electronic wave function in the various regions of the double well potential. A single-mode cw dye laser excites 2(A) (1)Sigma(+)(v(A),J) approximately 1(b) (3)Pi(Omega=0)(v(b),J) mixed singlet-triplet "window" levels from thermally populated rovibrational ground state levels, 1(X) (1)Sigma(+)(v(X),J+/-1). Further excitation by a single-mode cw Ti:sapphire laser selects various 3 (3)Pi(0)(v(Pi),J(Pi)) rovibrational levels, which are detected by observing direct 3 (3)Pi(0)-->1(a) (3)Sigma(+) fluorescence in the green spectral region. Using the inverse perturbation approximation method, we have determined a 3 (3)Pi(0) potential curve that reproduces the measured energies to approximately 0.24 cm(-1). In addition, the hyperfine and spin-orbit constants, b(F) and A(v), have been determined for each region of the potential curve.     

Spin-forbidden transitions in the vicinity of the 2 (1)pi(u) <-- X (1)sigma(g)+ band system of Rb2

We have investigated the Rb2 475 nm system by resonance enhanced two-photon ionization spectroscopy in a pulsed molecular beam. Strong extra bands accompanying the 2 (1)Pi(u) v' = 5 - 8 <-- X (1)Sigma(g)(+) v' = 0 bands were newly observed. Rotational analysis of the main and extra bands reveals that the 2 (1)Pi(u) v' = 5 - 8 levels are significantly perturbed, mainly by the 3 (3)Sigma(u)(+)(1 u) state and also by the 2 (3)Pi(u)(1 u) state. For the major perturber, 3 (3)Sigma(u)(+)(1 u), the intensity borrowing has been found to be facilitated by the 2 (1)Pi(u)-3 (3)Sigma(u)(+)(1 u) potential energy curve crossing near 21,100 cm(-1). For the vibronic-band intensities of the 2 (3)Pi(u)(1 u) v' <-- X (1)Sigma(g)(+) v' = 0 transitions observed in this spectral region, intensity borrowing was most effective when the 2 (3)Pi(u)(1 u) levels were close to the 3 (3)Sigma(u)(+)(1 u) levels. A deperturbation fit for the perturbing bands has provided the 2 (1)Pi(u)-3 (3)Sigma(u)(+)(1 u) coupling constants.     

Photodissociation dynamics of N2O at 130 nm: the N2(A 3Sigmau +,B 3Pig)+O(3PJ = 2,1,0) channels

Oxygen Rydberg time-of-flight spectroscopy was used to study the vacuum ultraviolet photodissociation dynamics of N(2)O near 130 nm. The O((3)P(J)) products were tagged by excitation to high-n Rydberg levels and subsequently field ionized at a detector. In agreement with previous work, we find that O((3)P(J)) formation following excitation to the repulsive N(2)O D((1)Sigma(+)) state produces the first two electronically excited states of the N(2) counterfragment, N(2)(A (3)Sigma(u) (+)) and N(2)(B (3)Pi(g)). The O((3)P(J)) translational energy distribution reveals that the overall branching ratio between N(2)(A (3)Sigma(u) (+)) and N(2)(B (3)Pi(g)) formation is approximately 1.0:1.0 for J = 1 and 2, with slightly less N(2)(B (3)Pi(g)) produced in coincidence with O((3)P(0)). The angular distributions were found to be independent of J and highly anisotropic, with beta = 1.5+/-0.2.     

Time-resolved study of excited states of N2 near its first ionization threshold

Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing (1)Σ(g)(-) state has been excited via the intermediate c(4) (v = 0) (1)Π(u) Rydberg state. We present the analysis of the band located at T(v) = 10,800.7 ± 2 cm(-1) with respect to the intermediate state, 126,366 ± 11 cm(-1) with respect to the ground state, approximately 700 cm(-1) above the first ionization threshold. From the analysis a rotational constant of B(v) = 1.700 ± 0.005 cm(-1) has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c(4) (0) and c(5) (0) states are 5.6 and 4.4 ns, respectively, while the b(') (12), c(')(4) (4, 5, 6), and c(')(5) (0) states all have lifetimes in the range of hundreds of picoseconds.     

Ultrafast decay of superexcited c 4Σu- nlσg v=0,1 states of O2 probed with femtosecond photoelectron spectroscopy

Neutral superexcited states in molecular oxygen converging to the O(2)(+) c (4)Σ(u)(-) ion state are excited and probed with femtosecond time-resolved photoelectron spectroscopy to investigate predissociation and autoionization relaxation channels as the superexcited states decay. The c (4)Σ(u)(-) 4sσ(g) v=0, c (4)Σ(u)(-) 4sσ(g) v=1, and c (4)Σ(u)(-) 3dσ(g) v=1 superexcited states are prepared with pulsed high-harmonic radiation centered at 23.10 eV. A time-delayed 805 nm laser pulse is used to probe the excited molecular states and neutral atomic fragments by ionization; the ejected photoelectrons from these states are spectrally resolved with a velocity map imaging spectrometer. Three excited neutral O* atom products are identified in the photoelectron spectrum as 4d(1)?(3)D(J)°, 4p(1) (5)P(J)° and 3d(1) (3)D(J)° fragments. Additionally, several features in the photoelectron spectrum are assigned to photoionization of the transiently populated superexcited states. Using principles of the ion core dissociation model, the atomic fragments measured are correlated with the molecular superexcited states from which they originate. The 4d(1) (3)D(J)° fragment is observed to be formed on a timescale of 65 ± 5 fs and is likely a photoproduct of the 4sσ(g) v = 1 state. The 4p(1) (5)P(J)° fragment is formed on a timescale of 427 ± 75 fs and correlated with the neutral predissociation of the 4sσ(g) v = 0 state. The timescales represent the sum of predissociation and autoionization decay rates for the respective superexcited state. The production of the 3d(1) (3)D(J)° fragment is not unambiguously resolved in time due to an overlapping decay of a v = 1 superexcited state photoelectron signal. The observed 65 fs timescale is in good agreement with previous experiments and theory on the predissociation lifetimes of the v = 1 ion state, suggesting that predissociation may dominate the decay dynamics from the v = 1 superexcited states. An unidentified molecular state is inferred by the detection of a long-lived depletion signal (reduction in autoionization) associated with the B (2)Σ(g)(-) ion state that persists up to time delays of 105 ps.     

Quadrupole, octopole, and hexadecapole electric moments of Sigma, Pi, Delta, and Phi electronic states: cylindrically asymmetric charge density distributions in linear molecules with nonzero electronic angular momentum

The number of independent components, n, of traceless electric 2(l)-multipole moments is determined for C(infinity v) molecules in Sigma(+/-), Pi, Delta, and Phi electronic states (Lambda=0,1,2,3). Each 2(l) pole is defined by a rank-l irreducible tensor with (2l+1) components P(m)((l)) proportional to the solid spherical harmonic r(l)Y(m)(l)(theta,phi). Here we focus our attention on 2(l) poles with l=2,3,4 (quadrupole Theta, octopole Omega, and hexadecapole Phi). An important conclusion of this study is that n can be 1 or 2 depending on both the multipole rank l and state quantum number Lambda. For Sigma(+/-)(Lambda=0) states, all 2(l) poles have one independent parameter (n=1). For spatially degenerate states--Pi, Delta, and Phi (Lambda=1,2,3)--the general rule reads n=1 for l<2/Lambda/ (when the 2(l)-pole rank lies below 2/Lambda/ but n=2 for higher 2(l) poles with l>or=2/Lambda/. The second nonzero term is the off-diagonal matrix element [formula: see text]. Thus, a Pi(Lambda=1) state has one dipole (mu(z)) but two independent 2(l) poles for l>or=2--starting with the quadrupole [Theta(zz),(Theta(xx)-Theta(yy))]. A Delta(Lambda=2) state has n=1 for 2((1,2,3)) poles (mu(z),Theta(zz),Omega(zzz)) but n=2 for higher 2((l>or=4)) poles--from the hexadecapole Phi up. For Phi(Lambda=3) states, it holds that n=1 for 2(1) to 2(5) poles but n=2 for all 2((l>or=6)) poles. In short, what is usually stated in the literature--that n=1 for all possible 2(l) poles of linear molecules--only applies to Sigma(+/-) states. For degenerate states with n=2, all Cartesian 2(l)-pole components (l>or=2/Lambda/) can be expressed as linear combinations of two irreducible multipoles, P(m=0)((l)) and P/m/=2 Lambda)((l)) [parallel (z axis) and anisotropy (xy plane)]. Our predictions are exemplified by the Theta, Omega, and Phi moments calculated for Lambda=0-3 states of selected diatomics (in parentheses): X (2)Sigma(+)(CN), X (2)Pi(NO), a (3)Pi(u)(C(2)), X (2)Delta(NiH), X (3)Delta(TiO), X (3)Phi(CoF), and X (4)Phi(TiF). States of Pi symmetry are most affected by the deviation from axial symmetry.     

Observation of the nd 1Delta(g) (n = 6, 7, and 8) Rydberg states of Na2 by optical-optical double resonance spectroscopy: L uncoupling and perturbations

The nd (1)Delta(g) (n = 6, 7, and 8) Rydberg states of Na(2) correlating with the asymptotic limits of Na(3s) + Na(nd) have been observed using high-resolution cw optical-optical double resonance spectroscopy corresponding to the rovibrational transitions X (1)Sigma(g)(+)(v("),J(")) + h nu(pump) --> B (1)Pi(u)(v('),J(')) + h nu(probe) --> nd (1)Delta(g)(v,J). Totals of 104, 83, and 45 identified rovibrational e/f-parity levels in the ranges of v = 0-11, 11 < or = J < or = 83; v = 0-10, 11 < or = J < or = 83; and v = 0-10, 11 < or = J < or = 65, have been assigned to the 6d (1)Delta(g), 7d (1)Delta(g), and 8d (1)Delta(g) states, respectively. Using the observed quantum levels, molecular constants were determined from the Dunham fits of the e-parity levels and the Rydberg-Klein-Rees potential curves were constructed for the nd (1)Delta(g)(n = 6-8) states. The characteristics of the estimated Lambda-doubling splitting constants (q(0), q(v), and mu) with n(= 5-8) of the nd (1)Delta(g) series have been explored. Detailed investigations reveal that the nd (1)Delta(g)(n = 6-8) states involve L uncoupling from the internuclear axis and each of these states is affected by an asymmetric perturbation caused by the up and down adjacent states. The rotational-branch intensity and position anomalies in the observed spectra of the nd (1)Delta(g) series (n = 5-8) of Na(2) lead to the conclusion that due to the effects of the L-uncoupling perturbations, the same l complexes approaching the same ion-core limits result in the same l-mixing processes which lead to the formation of the supercomplexes due to the anisotropy of the molecular-ion [Na(2)(+)(3s)] field. This would open up opportunities to study the effects of L uncoupling and perturbations in the nd series and high Rydberg states of other alkali dimers.     

Inclusion Compounds of Thiourea and Peralkylated Ammonium Salts. Part V. Hydrogen-Bonded Host Lattices Built of Thiourea and Acetate Ions

New inclusion complexes (C2H5)4N+CH3CO-°*4(NH2)2CS(1), (n-C3H7)4N+[(CH3CO2)2H]-°2(NH2)2CS (2), (n-C4H9)4N+[(CH3CO2)2H]-°2(NH2)2CS (3) and (CH3)4N+CH3CO2-°(NH2)2CS(4) have been prepared and characterized by X-raycrystallography. Crystal data, MoK radiation: 1, space groupC2/c, a = 28.702(4), b = 8.457(1), c =22.906(7) Å, = 98.91(1)°, Z = 8, and RF = 0.048for 2587 observed data; 2, space group P2/n, a = 8.536(2), b = 8.613(1), c = 18.360(2) Å, = 90.66(2)°, Z = 2, and RF = 0.045 for 1637 observed data; 3,space group P¯1, a = 8.771(3), b = 10.720(1), c = 16.742(2) Å, = 99.08(6), = 94.07(2), = 95.25(2)°, Z = 2, and RF = 0.063 for 2736 observed data; 4, space group P21/n, a = 8.421(3), b = 16.532(6), c = 8.628(3) Å, = 90.25(3), Z = 4, and RF = 0.050 for 1507observed data. In the crystal structure of 1, the thiourea moleculesand acetate ions constitute two channel systems aligned parallel to the[110] and [¯110] directions, with thetetraethylammonium cations accommodated in a single column withineach channel. In the crystal structure of 2, hydrogen-bondedcentrosymmetric thiourea dimers and acetate dimers are alternatelyarranged to form a zigzag, puckered ribbon running parallel to [10¯¯1], and the stacked columns of cations are sandwichedbetween undulatory wave layers constructed from the parallelarrangement of [((NH2)2CS)2((CH3CO2)2H)-] ribbons. In the crystal structure of 3,zigzag hydrogen-bonded thiourea ribbons are linked by dimeric acetateanions existing in two different conformations to generate puckeredlayers matching the (002) planes, and the (n-C4H9)4N+ cations occupy the intervening space. Incompound 4 the cations are accommodated in pseudo-channelsgenerated from infinitely extended thiourea-acetate composite ribbons.     

Photodissociation channels for N2O near 130 nm studied by product imaging

The photodissociation of N(2)O at wavelengths near 130 nm has been investigated by velocity-mapped product imaging. In all, five dissociation channels have been detected, leading to the following products: O((1)S)+N(2)(X (1)Sigma), N((2)D)+NO(X (2)Pi), N((2)P)+NO(X (2)Pi), O((3)P) + N(2)(A (3)Sigma(+) (u)), and O((3)P) + N(2)(B (3)Pi(g)). The most significant channel is to the products O((1)S) + N(2)(X(1)Sigma), with strong vibrational excitation in the N(2). The O((3)P) + N(2)(A,B):N((2)D,(2)P) + NO branching ratio is measured to be 1.4 +/- 0.5, while the N(2)(A) + O((3)P(J)):N(2)(B) + O((3)P(J)) branching ratio is determined to be 0.84+/-0.09. The spin-orbit distributions for the O((3)P(J)), N((2)P(J)), and N((2)D(J)) products were also determined. The angular distributions of the products are in qualitative agreement with excitation to the N(2)O(D (1)Sigma(+)) state, with participation as well by the (3)Pi(v) state.