Determining the composition of the vacuum-liquid interface in ionic-liquid mixtures.

The vacuum-liquid interfaces of a number of ionic-liquid mixtures have been investigated using the combination of reactive-atom scattering with laser-induced fluorescence detection (RAS-LIF), selected surface tension measurements, and molecular dynamics (MD) simulations. The mixtures are based on the widespread 1-alkyl-3-methylimidazolium ([Cnmim]+) cation, including mixed cations which differ in chain length or chemical functionality with a common anion; and different anions for a common cation. RAS-LIF results imply that the surface compositions exhibit a general form of non-stoichiometric behaviour that mimics the well-known Henry's and Raoult's laws at low and high mole fraction, respectively. The extended Langmuir model provides a moderately good single-parameter fit, but higher-order terms are required for an accurate description. The quantitative relationship between RAS-LIF and surface tension, which probes the surface composition only indirectly, is explored for mixtures of [C2mim]+ and [C12mim]+ with a common bis(trifluoromethylsulfonyl)imide ([NTf2]-) anion. Extended Langmuir model fits to surface tension data are broadly consistent with those to RAS-LIF; however, several other common approaches to extracting surface compositions from measured surface tensions result in much larger discrepancies. MD simulations suggest that RAS-LIF faithfully reports on the alkyl-chain exposure at the surface, which is only subtly modified by composition-dependent structural reorganisation.

Parity-dependent oscillations in collisional polarization transfer: CN(A²Π, v = 4) + Ar.

We report the first systematic experimental and theoretical study of the state-to-state transfer of rotational angular momentum orientation in a (2)Π-rare gas system. CN(X(2)Σ(+)) was produced by pulsed 266 nm photolysis of ICN in a thermal bath (296 K) of Ar collider gas. A pulsed circularly polarized tunable dye laser prepared CN(A(2)Π, v = 4) in two fully state-selected initial levels, j = 6.5 F1e and j = 10.5 F2f, with a known laboratory-frame orientation. Both the prepared levels and a range of product levels, j' F1e and j' F2f, were monitored using the circular polarized output of a tunable diode laser via cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM Doppler lineshapes for co-rotating and counter-rotating pump-and-probe geometries reveal the time-dependence of the populations and orientations. Kinetic fitting was used to extract the state-to-state population transfer rate constants and orientation multipole transfer efficiencies (MTEs), which quantify the degree of conservation of initially prepared orientation in the product level. Complementary full quantum scattering (QS) calculations were carried out on recently computed ab initio potential energy surfaces. Collision-energy-dependent tensor cross sections for ranks K = 0 and 1 were computed for transitions from both initial levels to all final levels. These quantities were integrated over the thermal collision energy distribution to yield predictions of the experimentally observed state-to-state population transfer rate constants and MTEs. Excellent agreement between experiment and theory is observed for both measured quantities. Dramatic oscillations in the MTEs are observed, up to and including changes in the sign of the orientation, as a function of even/odd Δj within a particular spin-orbit and e/f manifold. These oscillations, along with those also observed in the state-to-state rate constants, reflect the rotational parity of the final level. In general, parity-conserving collisions conserve rotational orientation, while parity-changing collisions result in large changes in the orientation. The QS calculations show that the dynamics of the collisions leading to these different outcomes are fundamentally different. We propose that the origin of this behavior lies in interferences between collisions that sample the even and odd-λ terms in the angular expansions of the PESs.

Depolarization of rotational angular momentum in CN(A2Π, v = 4) + Ar collisions.

Angular momentum depolarization and population transfer in CN(A(2)Π, v = 4, j, F(1)e) + Ar collisions have been investigated both experimentally and theoretically. Ground-state CN(X(2)Σ(+)) molecules were generated by pulsed 266-nm laser photolysis of ICN in a thermal (nominally 298 K) bath of the Ar collision partner at a range of pressures. The translationally thermalized CN(X) radicals were optically pumped to selected unique CN(A(2)Π, v = 4, j = 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5, F(1)e) levels on the A-X (4,0) band by a pulsed tunable dye laser. The prepared level was monitored in a collinear geometry by cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM lineshapes for co- and counter-rotating circular pump and probe polarizations were analyzed to extract the time dependence of the population and (to a good approximation) orientation (tensor rank K = 1 polarization). The corresponding parallel and perpendicular linear polarizations yielded population and alignment (K = 2). The combined population and polarization measurements at each Ar pressure were fitted to a 3-level kinetic model, the minimum complexity necessary to reproduce the qualitative features of the data. Rate constants were extracted for the total loss of population and of elastic depolarization of ranks K = 1 and 2. Elastic depolarization is concluded to be a relatively minor process in this system. Complementary full quantum scattering (QS) calculations were carried out on the best previous and a new set of ab initio potential energy surfaces for CN(A)-Ar. Collision-energy-dependent elastic tensor and depolarization cross sections for ranks K = 1 and 2 were computed for CN(A(2)Π, v = 4, j = 1.5-10.5, F(1)e) rotational/fine-structure levels. In addition, integral cross sections for rotationally inelastic transitions out of these levels were computed and summed to yield total population transfer cross sections. These quantities were integrated over a thermal collision-energy distribution to yield the corresponding rate constants. A complete master-equation simulation using the QS results for the selected initial level j = 6.5 gave close, but not perfect, agreement with the near-exponential experimental population decays, and successfully reproduced the observed multimodal character of the polarization decays. On average, the QS population removal rate constants were consistently 10%-15% higher than those derived from the 3-level fit to the experimental data. The QS and experimental depolarization rate constants agree within the experimental uncertainties at low j, but the QS predictions decline more rapidly with j than the observations. In addition to providing a sensitive test of the achievable level of agreement between state-of-the art experiment and theory, these results highlight the importance of multiple collisions in contributing to phenomenological depolarization using any method sensitive to both polarized and unpolarized molecules in the observed level.

Rotationally elastic and inelastic dynamics of NO(X2Π, v = 0) in collisions with Ar.

A combined theoretical and experimental study of the depolarization of selected NO(X(2)Π, v = 0, j, F, ɛ) levels in collisions with a thermal bath of Ar has been carried out. Rate constants for elastic depolarization of rank K = 1 (orientation) and K = 2 (alignment) were extracted from collision-energy-dependent quantum scattering calculations, along with those for inelastic population transfer to discrete product levels. The rate constants for total loss of polarization of selected initial levels, which are the sum of elastic depolarization and population transfer contributions, were measured using a two-color polarization spectroscopy technique. Theory and experiment agree qualitatively that the rate constants for total loss of polarization decline modestly with j, but the absolute values differ by significantly more than the statistical uncertainties in the measurements. The reasons for this discrepancy are as yet unclear. The lack of a significant K dependence in the experimental data is, however, consistent with the theoretical prediction that elastic depolarization makes only a modest contribution to the total loss of polarization. This supports a previous conclusion that elastic depolarization for NO(X(2)Π) + Ar is significantly less efficient than for the electronically closely related system OH(X(2)Π) + Ar [P. J. Dagdigian and M. H. Alexander, J. Chem. Phys. 130, 204304 (2009)].

Elastic depolarization of OH(A) by He and Ar: a comparative study.

Two color polarization spectroscopy has been employed to measure the collisional depolarization of OH(A(2)Sigma(+), v = 1) by He and Ar. Complementary experiments using Zeeman quantum beat spectroscopy have also been performed to determine separately the cross sections for rotational energy transfer (RET) out of selected rotational levels of OH(A, v = 0) + Ar, as well as those for elastic depolarization. This has been achieved by dispersing the emission, so as to observe a single fluorescence transition. Elastic depolarization of OH(A) by Ar is found to be significant with that for loss of rotational alignment exceeding that for loss of orientation. In the case of OH(A) + He, the polarization spectroscopy measurements suggest that elastic depolarization plays a relatively minor role in the loss of the polarization signal compared with RET. The experimental data for OH(A) + Ar are compared in detail with the results of quasi-classical trajectory calculations that accommodate the effects of electron spin. These classical calculations are assessed against the results obtained using full close-coupled open shell quantum mechanical scattering methods. Overall the level of agreement between the two experiments, and between experiment and theory, is very reasonable. Surprisingly, at low N the elastic depolarization cross sections for OH(A) + Ar are found to be quite similar in magnitude to those observed for OH(X) + Ar despite the fact that the well depth in the latter system is considerably smaller than that for OH(A)-Ar. However, for OH(A) + Ar the depolarization cross sections are insensitive to N in the range 1-14. It is proposed that this behavior partly reflects the relatively anisotropic nature of the potential energy surface, which exhibits deep wells of different depths at the two linear configurations OH(A)-Ar and Ar-OH(A), and partly the nature of elastic depolarizing collisions, which must occur with a velocity component perpendicular to the plane of rotation of the diatomic molecule.

Service use and cost by mentally ill chemical abusers: differences by retention in a therapeutic community.

PURPOSE: Earlier research estimated the incremental costs and outcomes of a modified therapeutic community (modified TC) for mentally ill chemical abusers (MICAs) relative to a treatment-as-usual (TAU) control group. The present study extended the cost analysis by disaggregating the modified TC group into clients who completed the program (completers) and clients who dropped out (separaters). METHODS: Bivariate and multivariate analyses were conducted to estimate differences in treatment and other service costs among completers, separaters, and TAU. Subjects were sequentially assigned to the modified TC (n = 171) or TAU (n = 47), and the analysis period covered 12 months post-baseline. Using a standardized instrument to collect resource use and cost data, the estimated weekly cost per client in the modified TC was $554, with completers showing a larger average cost of treatment ($27,595) than separaters ($9,986). RESULTS: The average TAU subject had a much higher cost for other (non-modified TC) services ($29,795) relative to separaters ($22,048) or completers ($1,986). These findings suggest that, from baseline to the 12-month follow-up, the total cost of modified TC treatment and other services for completers may be slightly lower than the total cost for separaters or TAU subjects. Since the modified TC group had better outcomes than the TAU group, and the completers had better outcomes than the separaters, the modified TC program could be an effective mechanism to reduce the costs of service utilization as well as improve clinical outcomes. IMPLICATIONS: This detailed investigation into service utilization and cost provides policy-makers and program directors with valuable information regarding potentially cost-effective interventions and further underscores the importance of retention in treatment for this vulnerable population.

Modified therapeutic community for homeless mentally ill chemical abusers: treatment outcomes.

This study compared homeless mentally ill chemical abuser (MICA) clients (n = 342), male and female, sequentially assigned to either of two modified therapeutic community programs (TC1 and TC2) and to a treatment-as-usual (TAU) control group. Follow-up interviews were obtained at 12 months postbaseline and at time F (on average more than 2 years postbaseline) on a retrieved sample of 232 (68%) clients and 281 (82%) clients, respectively. Outcome measures assessed five domains: drug use, crime, HIV risk behavior, psychological symptoms, and employment. Individuals in both modified TC groups showed significantly greater behavioral improvement than TAU at 12 months and time F, and the modified TC2, with lower demands and more staff guidance, was superior to modified TC1. Completers of both TC programs showed significantly greater improvement than dropouts and a subgroup of TAU clients with high exposure (i.e., more than 8 months) to other treatment protocols. The present findings support the effectiveness and longer term stability of effects of a modified TC program for treating homeless MICA clients.

Modified therapeutic community for homeless mentally ill chemical abusers: emerging subtypes.

This paper is one of a series reporting on a clinical field trial evaluating the efficacy of the modified therapeutic community (TC) approach for the treatment of homeless mentally ill chemical abusers (MICAs). The social and psychological characteristics of the treatment sample were described in an earlier paper; the purpose of the present report was to categorize subtypes of homeless MICA clients to predict with greater accuracy their treatability in modified TCs. An index that consistently correlated with treatment-relevant variables was identified for each of three dimensions; Homelessness (residential instability), Mental Illness (current severity), and Substance Abuse (current substance abuse/dependence diagnosis). These indices yielded distributions that captured the variability in the sample with respect to a number of variables, including drug use, criminality, human immunodeficiency virus (HIV) risk (sexual behavior), psychological status, and motivation. Bivariate and multivariate analyses showed that the indices were not strongly related to demographic variables such as race/ethnicity, age, or gender, but were significantly associated with baseline drug use, criminal activity, HIV risk (sexual behavior), psychological symptoms, and motivation and readiness. These findings indicate that, even among those admitted to residential treatment for substance abuse, homeless MICA clients are not homogeneous; rather, subgroup differences emerge among the indices of homelessness, mental illness, and substance abuse. The efficacy of treatment in modified TCs for these subgroups will be assessed in subsequent papers examining the relationships among the three indices, client retention, and outcomes during and subsequent to residential treatment.

Modified therapeutic community for mentally ill chemical abusers: outcomes and costs.

Several studies have established that the personal and social consequences of substance abuse are extensive and costly. These consequences are frequently compounded by mental illness. Although interventions that target mentally ill chemical abusers (MICAs) present several challenges, the potential benefits of successful interventions are significant. This article presents outcomes and costs of a modified therapeutic community (TC) intervention for homeless MICAs. Outcomes at follow-up are compared with those for a control group of homeless MICAs receiving standard services in a "treatment-as-usual" (TAU) condition. Annual economic costs for the modified TC and the average weekly cost of treating a single client are estimated. Treatment and other health service costs at 12 months postbaseline are compared for modified TC and TAU clients. The results of this study indicate that, suitably modified, the TC approach is an effective treatment alternative for homeless MICAs, with the potential to be highly cost-effective relative to standard services.

Sequential assignment and treatment-as-usual. Alternatives to standard experimental designs in field studies of treatment efficacy.

Psychosocial treatment research studies encounter obstacles to random assignment (RA). Used together, two procedures offer an alternative to the standard RA design. First, sequential assignment (SA) may create less opposition from administration, staff, and clients. SA operates on the principle that limited bed availability, a common treatment consideration in the field, determines assignment of clients to conditions. Second, treatment-as-usual (TAU) represents an alternative type of control condition. Some clients on the waiting list will, before a slot opens up and they enter an experimental condition, be absorbed into the existing treatment system, in which the amount and type of treatment they receive can vary widely. Substituting SA and TAU for the standard RA design may introduce methodological impurities including certain limited biases.

Modified therapeutic community for homeless mentally ill chemical abusers. Sociodemographic and psychological profiles.

This paper, the first in a series of reports from a field study on the efficacy of modified therapeutic community (TC) treatment for homeless mentally ill chemical abusers, presents sociodemographic profiles, psychiatric diagnosis, and psychological symptom data on 342 homeless mentally ill chemical abusing clients seeking treatment in mental health community residence settings. The findings reflect the multidimensional deficits, social dysfunctionality, and severity of psychopathology of the study sample. The paper discusses the implications of these findings for program design and program planning, with special reference to modified TC programs.

Therapeutic community methods in methadone maintenance (Passages): an open clinical trial.

A non-random open clinical trial was conducted to determine whether a day-treatment program based on modified therapeutic community (TC) methods (Passages) produced better treatment outcomes for heroin addicts than did standard methadone maintenance therapy. Altogether, 327 methadone clients at two clinic sites were studied: 115 Passages members, and 212 comparison subjects. Compared to non-Passages clients, clients who voluntarily joined and remained in Passages for at least 6 months exhibited significantly larger reductions in cocaine use, heroin use, needle use, criminal activity, and psychological dysfunction. The present findings suggest that TC-oriented enhanced day-treatment can help methadone clients recover from drug abuse and adopt a prosocial lifestyle.